Suppose that 6 J of work is needed to stretch a spring from its natural length of 28 cm to a length of 35 cm.
(a) How much work W is needed to stretch the spring from 38 cm to 43 cm? (Round the answer to the nearest hundredth.)
(b) How far beyond its natural length will a force of 25 N keep the spring stretched? (Round the answer to the nearest tenth.)