An edge crack is located at the mid$-$span, bottom part of a rectangular beam that is loaded by a two vertical forces $($F$)$ and one horizontal force $(10$F$)$ as shown in the figure.

Numerical data: Force $F=6000N,$ thickness $t=0\mathrm{.}02m,$ height $h=0\mathrm{.}032m,$ length $L=0\mathrm{.}04$ m $,{}_{\text{y}\text{i}\text{e}\text{l}\text{d}}=900$MPa, fracture toughness $K_{lc}=50$MPa.$m^{0\mathrm{.}5}$

Determine the critical crack size.Please do full exersize not just the equations