Answer :
[tex]C=\frac{1}{2}h(q+z)\\\\\frac{1}{2}h(q+z)=C\ \ \ \ |multiply\ both\ sides\ by\ 2\\\\h(q+z)=2C\\\\hq+hz=2C\ \ \ \ |subtract\ hz\ from\ both\ sides\\\\hq=2C-hz\ \ \ \ |divide\ both\ sides\ by\ h\neq0\\\\q=\frac{2C-hz}{2}[/tex]