Someone please help ASAP please do a. and b. or at least just do one of them for me thank you so much

Find the percent error of the measurement 4 cm

The product of (7x-2) and (20-3x)/4. when x=4

How many revolutions will a car wheel of diameter 28 in. make over a period of half an hour if the car is traveling at 60 mi/hr? the final answer is supposedly 21,609 but i have no idea how to get that, show work : )