William sold 6.84 litres of lemonade more than Susan.Tim sold 18.3 litres of lemonade more than Susan.William sold 21 litres of lemonade.

a)How many litres of lemonade did Tim sell?

b)How many litres of lemonade did they sell altogether?

amount sold by Susan ---- x L

amount sold by William ---- (x+6.84) L
amount sold by Tim ------ (x+18.3) L

a) solve x+6.84 = 21

b) add them up and sub in your solution for x