7. Suppose yogurt is on sale for $0.50 a piece, and you have a coupon for $0.30 off your total purchase. Write a function rule for the cost of n yogurts. How much would 20 yogurts cost?

the answer is a actually C(n) =0.5n-3 ; $9.70 and an equation for 20 yogurts is 20(n)=c50-30 i did this once and my answer was similiar to this.