In 9 weeks they each save 9×12=£108, so, in all, that’s £216.

Ground area of the tent is 2.5×4.2=10.5 sq m. This exceeds 10m², so the cost per night is £15. Sharing a tent for 5 nights is the same as for 4 nights, so that’s 4×15=£60. Another 5 nights costs the same, so total cost for the week is £120.

There are two people staying at a cost of £5 per night for 10 nights, so that’s £50 or £100 altogether. But if the special offer includes the person cost they only pay £40 each (paying for 8 nights at £5 per night per person) making £80 altogether.

Now add together both components: £120+£100=£220, so they will not have saved enough (£216), if the special offer doesn’t apply to the people.

But the special offer could make it £120+£80=£200, so they will save enough and have £16 saving.