Sam will be 12m behind when Robert crosses the finish line.
What does it mean to do speed?
I will assume the boys have all run at a constans speed right rom the beginning of the race.
When Robert has run 50, Sam has run 40 metres
so Sam has has run 4/5 as far as Robert.
If this ratio stays the same then when Robert has run 60m Sam will have run 4/5 of 60 = 48 metres.
So that Sam will be 12m behind when Robert crosses the finish line.
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