The weight of the crate is acting downward on the ground and the ground is exerting a force equal to the weight of the crate upward on the crate.
Draw a right triangle with sides 2.5N and the other side 6.5N. Using the pythagorean theorem, you can find the hypotenuse, which is the net force.c^2=2.5^2+6.5^2solve for c.
A balanced force means a net force of zero
Net force is 0 newtons because nothing is acting on the crate.