1. P = Q + 2R (Q)

I think that the subject is the one before the equal sign, therefore:

.....P - Q = Q + 2R - Q........subtract Q from both sides

P - Q - P = 2R - P..............subtract P from both sides

..........Q = -2R + P............multiply each componant by (-1)

..........Q = P - 2R..............rearrange