First, look at the key information from the question and form an equation for each of the first two sentences. These equations are as follows (let a represent the number of apples and b represent the number of bananas). Note that it is easier if you convert the prices to pence:
(1) 2a + 3b = 130
(2) 7a + b = 170
Next, you want to combine these equations in a way that eliminates either a or b. There are multiple ways of doing this. I would choose to first multiply (2) by 3 to form equation 3:
(3) 21a + 3b = 510
Then subtract (1) from (3) to form (4):
(4) 19a = 380
Solving (4) gives a = 20 (divide both sides by 19). If we rearrange (2) to make b the subject, then substitute a for 20, we get:
b = 170 - 7(20)
b = 170 - 140
b = 30
So the final answer is:
a) An apple costs 20p or £0.20b) A banana costs 30p or £0.30