5 biscuits cost 30p altogether how much do 7 biscuits cost?

First we want to find how much an individual biscuit costs.

If 5 biscuits costs 30p, then

5 x 1 biscuit = 30p

divide both sides by 5

1 biscuit = 6p

If one biscuit costs 6p, and we want to know how much 7 biscuits cost, then:

7 x 6p = 42p

7 biscuits costs 42 p