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Explanation:
Considering statement (a)., exactly two tours must depart after. Tour P but before Tour R, and so the departure sequence may be either PSTQR or PSQRT. Although three tours must arrive between Tour P and Tour R, three possible arrival sequence remain, depending on where Tour T fits into the sequence remain, depending on where Tour T fits into the sequence. Considering statement (b). Tour Q must depart immediately after Tour R, with tour T departing last and immediately between Tour Q and Tour S, resulting in only one possible arrival sequence- PSRQT. Similarly, Tour T must arrive third, and Tour R must arrive fifth, resulting in one possible arrival sequence - PQTSR.