Hi guys, i am currently preparing for one of my exams in hydraulics

.and here is the expression that I am failing to solve.

h/2 + L*h^3 / 12 * h * L * h/2

So my goal is to try to find a shorter expression for this.

and I get 2h/3

But our teachers solution is insisting on that it should be

h * 3/2

how did he get to that?