The Wronskian & Variation of Parameters · Easy problem

To solve $y''-y=4e^{t}$ by variation of parameters with $y_1=e^{t}$, $y_2=e^{-t}$, one uses $u_2'=\dfrac{y_1\,g}{W(y_1,y_2)}$ where $g=4e^{t}$. Find $u_2'(0)$.