SEE ATTACHMENT #1 for a diagram showing parameters.
PART a. Find the maximum value of P for which the box stays in contact with the floor.
PART b. Find the acceleration when this force is applied.
PART a. Step 1.
Creating or observing a careful diagram should be the first step of a solution. Observing ATTACHMENT #1, you note that the only forces on the box are P, N, and M g. ...
In a five step process, the problem is explained and solved.