Hooke's Law: Finding the Spring Constant with a 50g Mass and 7.0cm Stretch

[flyingpig]

Homework Statement

A 50g mass hangs at the end of a hookean spring. When a 20g more is added to the spring, it stretches 7.0cm more. Find the spring constant.

The Attempt at a Solution

Isn't it just

mg = kx

mg/x = k

Shouldn't m = 70g instead of 20g?

My key says m = 20g?

 

[Doc Al]

Shouldn't m = 70g instead of 20g?

That would give the total elongation from the unweighted position, not the additional elongation.