Acrate is hung from a spring with a force constant of 525 nm. this stretches the spring 0.30 m from its equilibrium position. what is the mass of the crate? use 10 m/s2

Lets use the expression

F = k*x  

Where k is the spring constant [N/m]

And x the distance from the equilibrium position.

This force is equal to the force due to the acceleration of gravity

F = k*x = m*g

F = 525[N/m]* 0.30 [m] = 157.5 [N]

157.5 [N] = m *10[m/s**2] > m = 15.75 kg

B. a circuit. i think