Answer:
12 + (1.50 multiplied by x)
Step-by-step explanation:
You have 12 dollars as the base. For every x days (x is the amount of how many days) he'd save $1.50. For one day, he'd save 1.50 plus his 12 dollars. Two days, he'd save 12 + (1.50 x x). Three, it'll be 12 + (1.50 x x) and so on.
I hope this helped. :)