Another Physics Question! (spider webs and flies)?

[tofuphysics]

Sorry for posting yet another physics question, but here it is:

A small fly of mass 0.25 g is caught in a spider's web. The web vibrates predominatly with a frequency of 4.0 hz.

What is the value of the effective spring stiffness constant k for the web?

At what frequency qould you expect the web to vibrate if an insect of mass 0.50 g were trapped?

And would you be so kind, anyone who answers, to post the equation or at least an explanation instead of just writing down an answer? Thanks so much!