Question

Supposed soda is on sale for $0.50 can and you have a coupon for $0.80 off your total purchase write a function rule for the cost of an cans of soda

Answer 1

If C is the cost and x the amount of cans.
C = 0.5x - 0.8

Answer 2

As per the problem

Soda is on sale for $0.50.

and you have a coupon for $0.80 off your total purchase.

we are supposed to write a function rule for the cost of an can of soda.

If you buy x cans of soda then the cost function can be written as

$C(x)=0.5x-0.80\\ \\ \text{we can replace x by the number of cans, here we have x=1 }\\ \\ C(1)=0.50*1-0.80$