Please help

[Yes]

I would get primary children to use something like the way I suggested.

I would do it a bit different. An adult fare is twice as a child fare. Two adult tickets are equal to 4 children. In total 7 children.
31.5/7=4.5 (children) then adult is 9.

Bu better to draw. Adult ticket - two blocks, child - one. You will have two double blocks and 3 single. 7 in total. Calculations are the same but this approach is more visual.

[yoyo123]

A diagram is always good!

[RedDevil66]

Mr and Mrs Black = 2 adult fares.

Child fare = 1/2 of adult fare so 3 children = 1.5 adult fares

so £31.50 for 3.5 adult fares

Fastest and most logical method