Firm A charges £24 up front then £0.60 for each kilometre. Firm B charges £39 up front then £0.35 for each kilometre. They cost the same at 60 kilometres. Which is cheaper for a 90 kilometre job?

1. At 90 kilometres, firm A costs 24 plus 0.60 times 90, which is 24 + 54, or £78. 2. Firm B costs 39 plus 0.35 times 90, which is 39 + 31.50, or £70.50. 3. Firm B is £7.50 cheaper at that distance. 4. Beyond the crossing point, the firm with the smaller charge per kilometre pulls ahead, and that is firm B at £0.35. 5. Option B states the reason correctly but names the wrong firm, since £0.60 is the larger rate. _Source: OpenStax College Algebra (CC BY 4.0), Ch 4 "Linear Functions", section 4.2 Modeling with Linear Functions_