Answer:

A box = $11
Explanation:
Given

Represent the first order with A and the second with B.
So, we have:

Solving (a): Find B.
To find B, we make use of:

Make B the subject

Substitute values for Total and A

Open bracket

Collect Like Terms


Solving (b): Cost of a box of light bulb
This means that:

Substitute 7x + 13 for Total

Collect Like Terms


Make x the subject

