Within the game you have the ability to do temp jobs in order to gain money/wealth. With that money you can buy items like a pillow to have a 50% to reduce stress by an additional point when you sleep or items that let you boost certain stats.

There is a total of five different temp jobs available and each one of these has different requirements and payouts. The game stores this information in the activities.rpy file. If you try to do an acitivity an invisible dice roll takes place and that needs to be higher than the invisible score for each job that is calculated as you do it.

Below you will find information about the dice roll as well as the jobs.

As it has been pointed out by @MasterForcer the Dice Roll happens in activities.py around line 4105.

The roll starts off as a number between 1 and 100 after which additional factors are taken into account to modify them. The two factors you can actively influence are the difficulty and your current luck. Difficulty is fixed for a given game while luck can be changed by various activitis. For the roll your luck is used to generate a number between either -Luck to 0 or 0 to Luck.

If you're sick there is an additional deduction of 15 points from the roll and on the easiest setting that is not creative you get a fixed bonus of 10. If you basically go for creative mode you will get a bonus of 10 million which pretty likely will always make you succeed.

Choosing the temp job at the arcade grants 2 money if it fails and 5 if you succeed. Being successfull is easier the more skillful you become at playing games by visiting the arcade. The number of visits and your current stress level are the governing stats.

Doing the job at the park grants 2 money on failure and 4 on success. The governing stats are stress and fitness. As stress doesn't have any multiplier attached to it, it's rather easy to beat.

The job at the shrine can net you between 2 (failure) and 4 (success) money. A special about failing it is that you will loose one point of affection for Sola. The governing stats are the number of times you have been to the shrine, your current stress and your fitness.

The temp job at the shopping mall will get you 7 money on success and 3 on failure. The governing stats are stress and charisma. Stress is multiplied by two and in addition a time based factor (the current month) is also added as a difficulty increase for your roll. As such this gets more difficult as the game progresses.

Doing the job at the science museum has the highest payout at 9 money on success while failing will still get you 4 money. At the same time it's the most difficult job. It has the highest base difficulty with a value of 40, the highest modifier to stress (2.5) and is not only based on the month you're in but also the week. As such it will get more difficult extremly quickly as the game progresses and the only stat to counter it is your inteligence.

The following table provides a summary of the payout on fail or success for each job and the formula found in the acitivies.rpy (slighty changed to make it fit).