Stupid physics problem.

[Stephen P]

For the box one, remember that

f = uN (N is normal force, perpindicular to the slope, pushing up on box)

To find normal force, resolve the weight (mg) of the box into components perpindicular and parralel to the slope, by taking the sin and cos of the angle.

F = ma = "forwards minus backwards and up minus down"
In this case, the weight vector parallel to the slope is the forward, and is being impeded by the backward force of friction (f = uN).

You might find it handy to know that whatever the mass of an object,
tan(@)= u (u is frictional coefficient, @ is angle of repose, the angle at which something begins sliding)