Dwayne's school lunch account balance is $75. Recently, he has been bringing lunch and only buys a drink, so he spends $1 every 5 days.
1. Write an equation in slope-intercept form to model Dwayne’s account balance as a function of time, in days.
2. Use the equation to determine how long it will take until Dwayne’s account needs more money put into it.
3. What does the slope represent in this context?