This is for the first answer and to be honest just use Desmos if you don’t have a graphing calculator
C is your answer! If you take away the 25.5 from 60 and divide that my 2 your answer is 17.25!
Cost/(number of cassettes) = $14.50/2 = x/15
Multiply by 15 to solve
15*($14.50/2) = x = $108.75
15 cassettes will cost $108.75.