The third expression is wrong
Step-by-step explanation:

Answer:
The answer is 17.2 hours
Step-by-step explanation: Because first you add all hours together (which is 86/15) then multiple it by 3 (week) which is 86/5 = 17.2 hours
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Answer:
Estimation is just giving a general answer to the situation and can be specified on specifics depending on the numbers used and whichever question it's asking. But also remember that whenever you estimate your answer will be an approximate answers, not an exact.