GCSE Edexcel Mathematics Practice Question

Hi there,

I'm a student going into Year 11, trying to attempt some problem-solving questions in mathematics. I have been stuck on a question for quite a while, and even knowing the answers does not help me work backwards.

Question:
Gary buys three mobile phone cases and two charging leads and pays £29.50. At the same time his friend buys two phone cases, but takes a charging lead back, gets a full refund and pays £11.50.
What is the cost of a mobile phone case? What is the cost of a charging lead?

The spoiler contains the answers. I would appreciate any help!

Thanks

Use some algebra to help and lay out the problem:

3c + 2l = 29.5
2c - l = 11.5

where c is the case and l is the lead


Now solve them simultaneously.