Answer:
At most 2 adult haircuts
Explanation:
The equation given is:

This equation dictates the number of haircuts Horace gives in 7 hours.
Horace gave 5 child haircuts (C=5). So, that would make the equation:

This means Horace can give LESS THAN or EQUAL to 2.6 haircuts.
2.6 haircuts doesn't make sense, so the maximum would be "2" haircuts.
Atmost 2 adult haircuts