Question

How do I find QS here?

Answer 1

Answer: 12.

To solve this problem, let's first solve for x. Thi is easiest done by figuring what QR is in terms of x using two equations, both from different lines.

In the first line:
QR = 15 - 4x.

In the third line:
QR = 13x - 1 - x = 12x - 1.

Now, we have to set these equations equal to each other. 
15 - 4x = 12x - 1
15 = 16x - 1
16x = 16
x = 1

Next, we take line three, 13x - 1, and substitute x as 1. The answer is 12.