homework and exercises - How do I use the signs in the spring force equation?

The spring force equation is F = - (k)(x). Assuming right direction of axis to be +ve, and left to be -ve, should we use the values of force and displacement, accordingly? And also, in this question -

"When a block is pulled out to x = +4.0 cm from 0.0 cm, we must apply a force of magnitude of 360 N to hold it here. Then find the spring constant."

So using F = - (k) (x) , we get (k) = - (F) (x), substituting values, k = - (360N) (4.0cm) . I.e., the spring constant comes out to be negative, why is it so? Please help , I am really confused with the sign convention.