2^2=4 so divid 36/4 is 9 and 4*2=8 now subtract 9-8=1 next 36/1 = 36 same on top is 8 now 36-8=28. 28 - 8 is 20 then 20-8= 12 answer is 12
To calculate the speed, divide 15.75 by 2.25 and you get 7 mph.
This type of sampling would be Random Sampling.