This problem seems like a lot when you read through it, but when you start to analyze the problem, the whole first line is extra information that we don't actually need. The part we really need to pay attention to is:
"p = qr - f, write the equation with q solved in terms of p, r, and f."
So, all we are doing here is some manipulating of the equation to get what we want. So, if p = qr - f, we can isolate the variable (q), to get p + f = qr. Now all we have to do is divide both sides by r to isolate the variable (q) even further, and we get
or [tex]$r=\frac{p+f}{r}$[tex]