The PE at the start would be the same as the KE just before impact = 0.5 mv^2 = 0.5 * 0.045 * 7.1 * 7.1 = 1.134 J
After the first bounce, KE = 0.5 * 0.045 * 3.9 * 3.9 = 0.342 J. This will convert back into PE at the top of the bounce meaning that the PE has changed from 1.134 to 0.342 i.e. 30% of the original value. It bounces two more times - each time losing 30% of its value so you can work it out from there.