I know i keep posting these sort of questions, its just not clicked yet.

A particle P is on a horizontal plane. Three horizontal forces of magnitude 7N, 10N and 6N, acting in directions as shown in the diagram, are applied to P.

a) show that the resultant of these 3 forces has a magnitude of approximately 6.25N, and find the angle between its direction and that of the 7N force.

b) the particle P has mass 2.5 kg and the coefficient of friction between P and the plane is 0.1. Assuming that the magnitude of the resultant of the three forces is 6.25N, calculate the magnitude of the acceleration of P.

I'm not sure where to even start with this.

I work out

10 = 6cos30

7=6sin30

but what do i do next? i don't really understand the question?