1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution The 4 main equations are equations (1), (2), (7) and (8). But I can't seem to isolate A5 alone as solving equations (7) and (8) will make A5 disappear.. I got the relation between A1, A2, A3 and A4 but still no A5..