aqa physics as unit 2 june 2010

Hi Im unsure of the equation used to derive an answer in this exam can anyone explain the calculation or what the formula used is?

Figure 4 shows a gymnast trampolining

(figure of a girl in the air at point B, and a girl at point A which is on a stretched trampoline)

In travelling from her lowest position at A to her highest position at B, her centre of
mass rises 4.2 m vertically. Her mass is 55 kg.
4 (a) Calculate the increase in her gravitational potential energy when she ascends from
position A to position B.
I worked out this using Ep=mgh (2266J)
4 (b) The gymnast descends from position B and regains contact with the trampoline when it
is in its unstretched position. At this position, her centre of mass is 3.2 m below its
position at B.
4 (b) (i) Calculate her kinetic energy at the instant she touches the unstretched trampoline.
I cannot work out this answer and how they got to it

4 (b) (ii) Calculate her vertical speed at the same instant.

this one must found by rearranging Ek=1/2mv^2 but Ek needed from bi)

so to work out bi) i need to use an equation to find out Ek but its not using the Ek=1/2mv^2 equation so what equation was used?

The mark scheme does 3.2/4.2 X 2264 why have the done this?