can anyone answer the question on the pic.....
Solve the following two equations simultaneously for $\displaystyle c$:
$\displaystyle \frac{c}{2 \sqrt{x}} = \frac{1}{2}$ .... (1)
$\displaystyle c \sqrt{x} = \frac{1}{2} x + \frac{9}{2}$ .... (2)
(Your other job, apart from solving these two equations, is to think about where they have come from).