solve h=-b/2a for b this is a algebra question
\(h=-\frac{b}{2a}\\\\\frac{b}{2a}=-h\ \ \ \ |multiply\ both\ sides\ by\ 2a eq0\\\\\huge\boxed{b=-2ah}\)
\(\sf Solve \ for \ b. \\ \\ h = \frac{-b}{2} a \\ \\ Flip \ equation \\ \\ \frac{-1}{2} ab = h \\ \\ Divide\ both \ sides\ by \frac{(-a)}{2} \\ \\ \frac{1}{2}ab/ \frac{-a}{2} = h / -a / 2 \\ \\ b = \frac{-2h}{a}\)