Forces of 2.4 N and 1.8 N act on an object at right angles to one another. What is the magnitude of a third force acting on the same object so that it remains stationary?

Question

A) 3.0 N
B) 4.2 N
C) 0.6 N

I don't understand how the answer is A)

Answer 1

equilibrant=-sqrt(2.4^2+1.8^2)

but if you have a keen eye, you recognize this as a 3,4,5 triangle, so the equilibrant is 30 (5*6), legs of triangle are 3*6, 4*6

Answer 2

oops, 3.0