Basically, this problem wants you to solve the area of the trapezoid given those dimensions, then multiply this to the unit cost to determine the total cost. The formula for the area of trapezoid is written below:
A = (a+b)h/2, where a and b are the lengths of the two bases
A = (15+9)(10)/2 = 120 cm²
Total Cost = 120 cm² * $0.80/cm² = $96