Solve

y+3y4y=0,y(0)=1,y(0)=11\displaystyle {y}{''}+{3}{y}'-{4}{y}={0},\quad{y}{\left({0}\right)}=-{1},\quad{y}'{\left({0}\right)}=-{11}

y(t)\displaystyle {y}{\left({t}\right)} =