Set up a formula that expresses the situation. 3+1.25n=10 where n is the number of additional hours.
Solve it for that n, and then add 1 to n because n is only the number of additional hours after the first.
3+1.25n=10 ---> 1.25n = 7 ---> n = 5.6. 5.6+1 = 6.6. But the problem doesn't indicate you can pay for part of an hour, so round down to 6 hours.
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