#### bobbym wrote:

First I must ask a question:

If you saw this in a book,

would you ask someone how they did it by hand?

No of course not! I would use a calculator!

But do you see what I mean? It is not the solution, but I am really bad at substituting/manipulating the formulas in the way required, so this is a real chance for me to see the method used. There was a lot before that step to get to those two equations, then the 'answer' is to express them in terms of qh and ql. However, I cannot do that and really need help. Will you not help me? I just cannot rearrange/manipulate.