Could I please have help (3m+5)-(6+5m)

Aflute is on sale for 20% off. including the discount and 8% tax, the sales price is $216.

Two cars which are 40 miles apart start moving simultaneously in the same direction with constant speeds. if the speed of the car which is behind is 56 mph and the speed of the other car is 48 mph, how many hours will it take for the car which is behind to catch up the car ahead of it?

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