This task is on the NRICH website. It is a group task requiring some preparation in printing and assembling sets of information. Much of the information is about using rates: work rates, material rates, price rates.
When groups complete this task their reasoning is often ad hoc, especially in the excitement of a group task. If there is a requirement to record their reasoning in order to keep track of their thinking, these work records can be used later as raw material for presenting more formal ways of setting out their work.
It is likely that some additive reasoning will be used, and doubling and halving, but all of these can be re-expressed as scaling – as multiplications – and learners can compare these notations and methods with the ways they reached their group conclusions.