Arnold wants to have $90 to buy his mom's birthday present. He puts the same amount of money into a jar each evening. The table shows
how much money is in the jar each evening for the first week.
X : each day 0, 1, 2, 3, 4, 5, 6
Y: $in the jar $9, $9.75, $10.50, $11.25, $12, $12.75,
$13.50
Write a function that can be used to calculate how much money Arnold has in the jar on any given day.