Please help I’m talking a test!!

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Twelve less than a number is at most 20

Thanh and her crew are building a stage in the shape of a trapezoid for an upcoming festival. the lengths of the parallel sides of the trapezoid are 14 ft and 24 ft. the height of the trapezoid is 12 ft. what is the area of the stage? enter your answer in the box. ft²