Graphing/Solving Differential Equation

I tried to solve it by using dsolve, however I'm not even sure if I'm doing it right. How do I get it in terms of x? Would the equivalent equation to the 2nd ODE in that picture be D2y=-P*t/bstiff

 syms bstiff P t L

    def=dsolve('D2y=-P*t/bstiff','y(L)=0','Dy(L)=0')

    slope=diff(def)

   L = 2.0;

   edef=subs(def)
   eslo=subs(slope)

   f = symfun(eslo + edef, t);

   bstiff = 1.0; P = 1.0; 
   ef = subs(f);

 fplot(ef, [0 L])
  end

[Birdman]

Have you tried my answer?