as you can see in A .... per hour cost is 20 dollars , so when you use test for 1 hr you have to pay 20 dollars , for two hours 40 dollars and for three hours 60 dollars !
in B....per hour cost is 25 dollars , so for 1 hr you have to give 25 , for two hours it's 50 , for three hours it would be 75 dollars !
so the result and the summary is:
if you use B for 4 hrs , you don't have to give any money due to coupon ! And after 4 hrs you have to give money !
so cost of 1 hr of A = cost of 4+ hrs of B
thus B is good for use !
{numerically}
if you want exact value :
25h-100=20h
h= 20
therefore , for 20 hrs , B is cheaper than A !
