This question only deals with paragraph 4, as said in the question.
A – Wrong
There is no information about part time jobs of people in their 60s and hence this is irrelevant.
B – Wrong
The statement given in this option is assumed and cannot be definitely proven. The wages are not given so we cannot work it out.
C – Wrong
Again, same assumption is made in this option as in B.
D – Correct
This is the only option left. If we work out the maths, then we get the same answer. We can use the formula given in the question. Let us round up the £8.82 value to £9
(15-9)/15 x 100 = %
6/15 x 100 = 40%
This percentage is roughly the same as the 41.2% given in paragraph 4. So this is the correct answer.