There are several ways in solving quick the 20% of any bill. One of those ways is by getting first the 10% of the amount then will later on be multiplied by two. Another one is by simply dividing the total bill amount by 5, which also 20% of the total bill amount. Hope this helps.
Your answer to the question is A
Multiply the two as area is base times height.
70 is the answer i did the math
