18. When Ellen went to the shop, she found she could spend all her money on 6 cans of cola and 7 croissants or on 8 cans of cola and 4 croissants. If she decided to buy only croissants, how many croissants could she buy?
A 12
В 13
C 15
D 16
E 25
18. D Let the cost of a can of cola be $x$ pence and the cost of a croissant be $y$ pence. The information in the question tells us that $6 x+7 y=8 x+4 y$ and that both sides of the equation represent the total amount of money Ellen has. Hence $3 y=2 x$. Therefore the total amount of money she has is $3 \times 3 y+7 y$ pence $=16 y$ pence. Hence she could buy 16 croissants if she bought only croissants.