If the coefficient of static friction is 0.15, then 0.15 of the crate's weight
shows up as a force resisting the horizontal pull. So we really only
need to know the crate's weight.
Weight = (mass) x (gravity) = (25) x (9.8) = 245 newtons.
0.15 of 245 newtons = 36.75 newtons.
The force due to friction that's holding the crate back, not letting it start
sliding, is 36.75 newtons. If you push it with 75 newtons of force, then
that IS enough to make the crate accelerate.
