That is an awful lot of Q's for one post !
1. Circumference of wheel = pi * d (inches) distance travelled for each wheel is pi * d * rpm (inches per min)
26 inch wheel pi * 26 x 200 = ~~16336.3 inches per minute
YOU do the 20 inch wheel
2.This is a conversion from in/min to mile/hr
26 inch wheel 16336.3 in / min x 1 ft / 12 in x 1 mile / 5280 ft x 60 min / hr = 15.5 m/hr
YOU do the 20 inch one