Finding the mother's mass from the spring oscillation periods

[phySicNewB]

The world's least exciting carnival ride consists of a cloth sling (of negligible mass) hanging by a spring of force constant k = 225 N/m. Children sit in the sling and bob up and down slowly. How exciting ...

Little Sally tries the ride. She gets into the sling, and, after Cletus the Carny gives her a bit of a push, oscillates up and down with a period of 1.78 seconds.

"Mommy, mommy, help, it's scary!" cries Sally. Her mother replies, "Don't worry, dear, you can sit on my lap and we'll ride together."

Together, Sally and her mother bob up and down with a period of 3.32 seconds.

Cletus scratches his head for a moment, then derives the mass of Sally's mother. What is it?

 

[hage567]

What have you attempted so far? You must have some idea of how to approach the problem. If not, tell us what you don't understand.