I think its D
Explanation:
Answer:
(a)
Expression:
Amount you earn per hour: $3
(b)
Expression: 
Amount you spend on shirt: $18
Step-by-step explanation:
(a)
Let x represent the amount you earn per hour.

(b)
Let s represent the amount you spent on a shirt.

Multiply both sides by 2 to get rid of the fraction on the right side:

Divide both sides by h to get b by itself. The following expression will be your answer:
Answer:
7
Step-by-step explanation:
Given,
3 Piles = 21 cards
1 Pile = (21 ÷ 3) cards
= 7 cards.