im stuck on question 2 part ii

using the formula f=ma and resolving the mg(weight of block) to its vertical component i got the equation mgcosa-R=m(Bsina) where b is resolved the acceleration of block caused by the acceleration of the wedge. i dont take into account its acceleration down the block.

looking at forces on the wedge and again using F=ma i get the equation Rsina=4(mB) subbing these into each other(isolate B) i get 4mgcosa-4R=R*sina^2