We know that the force formula for the inclined surface is given by:

F= m*g* sin(35) such that m= mass of the block , g is the gravity, and 35 is the inclined angle.

==> F = 20 * 9.8 * sin 35

==> F = 20*9.8*0.5736

==> F = 112.42 N

Then, the force that brings the block down is 112.42 N. Then we need an equal force but in the opposite direction.

Then, the force needed to prevent the block from moving is (112.42)N is oppsit direction.