Check the question again. I think the following is the intent of the question:
Force due to wt of block acting downward along the inclined surface = 6 x 10 sin(30) = 30N
Force due to friction acting downward along the inclined surface = 0.4 x 6 x 10 cos(30) = 20.78N
Net force acting downwards ~ 30 + 20 = 50N
If external force applied = 50N then block will be stationary
In order for the block to move exyternal force must be more than 50N. Once the block begins to move a constant 50N of force will be required to keep the blcok moving with a constant speed.