$\text{Solution The equation }$
$U_{tt}=4U_{xx}-U_t, 0<x<3,t>0\\ U(0,t)=U(3,t)=0,t>0\\ U(x,0)=e^x,U_t(x,0)=0,0<x<3$
when we use variable and separable U(x,t)=X(x)T(t) i get solutions for the $X_n(x)$ but i have faced problem with finding $T_n(t)$ can any one please help me with this part