Jonah received $300 in cash gifts for his fourteenth birthday. the function y remaining after x week if jonah spends $25 each week. graph the function and determine the amount remaining after 9 week

Assume that y its Jonah's cash and its initially 3000
y=300
But he spends 25/week. Assume that x is number of weeks.
y=300-25*x - its our function
If we want to find Jonahs cash after 9 week we have to substitute x=9, so
y=300-25*9
y=300-225
y=75$ - its the result