The Chief Examiner reported that this question was popular among the Candidates’ as they did well but had little problem in part (b).
In part (a), they did as expected by expressing as improper fractions  , then made use of BODMAS to get . Simplifying to get 5.
In part (b), they started by expressing  which is the same as |PR| = 3 cm. Then,  which can be simplified to x =  cm.