What is the net force on the block immediately after it starts to slide?

[AIMheels22]

Homework Statement

The coefficient of static friction between a block and a horizontal floor is 0.40, while the coefficient of kinetic friction is 0.15. The mass of the block is 5.0 kg. A horizontal force is applied to the block and slowly increased. What is the value of the applied horizontal force at the instant that the block starts to slide?

What is the net force on the block immediately after it starts to slide?

Homework Equations

The Attempt at a Solution

I am absolutely stumped by this problem! After a FBD i don't really know where to start, Please some one help me!

 

[Kurdt]

The instant the block starts to slide the applied force will be equal to the static friction force. How do you work out the static friction force?