Mechanics question on Simple Harmonic Motion in strings

A light elastic string of natural length 20cm and modulus 40N has one end attached to a fixed point A on a smooth horizontal surface and a body of mass 2kg attached to the other end. The body is held on the surface at a point which is 40cm from A, and released. Show that the subsequent motion will be periodic and find the time period of the motion and the speed of the body as it passes through A.

The answer for the time period is (2+pi)/5 seconds and the max speed is 2 m/s. Could someone please show me how to go about this question since I am having difficulty coming up with those answers.