Correct. The pool will have $\displaystyle{2}{x}+{20}\usepackage{cmbright}\Huge\$ gallons in $\displaystyle{x}\usepackage{cmbright}\Huge\$ minutes, so it will be full when $\displaystyle{2}{x}+{20}={50}.\usepackage{cmbright}\Huge\$ This happens when $\displaystyle{2}{x}={30},\usepackage{cmbright}\Huge\$ so $\displaystyle{x}={15}.\usepackage{cmbright}\Huge\$