The homogeneous rectangular block having dimensions a$=1\mathrm{.}90,$ b$=2\mathrm{.}86$ as shown, and mass m$,$ rests on the inclined plane which is hinged about a horizontal axis through O$.$ Calculate the minimum value of the coefficient of static friction between the block and the plane, if the block does not slip before tipping.

b$,$ hight of block

a$,$ width of block

$..........$

I believe that the solution shown is wrong as the equation for tipping is wrong and should be: mg$$ sin$($theta$)$ b$/2=$ N$$a$/2$