Answer: 160 hours
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Step-by-step explanation:
He earns $10.00 an hour. Let x be the number of hours worked in a month. So 10x represents how much he earns after working x hours.
If he spends $800 per month on fixed expenses, and wants this to be 50% of his total earnings, then this must mean that the other 50% is for other things (eg: spending on a vacation or putting it to savings). So his goal is to earn 800+800 = 1600 dollars per month.
Set 10x equal to this and solve for x
10x = 1600
x = 1600/10
x = 160
He needs to work 160 hours a month.
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Extra info:
Divide 160 over 4 (the approximate number of weeks in a month) and we see that he'll need to work 160/4 = 40 hours a week
If he only works Monday through Friday, that's 5 days of the week. So he'll put in 40/5 = 8 hours per day.
So his goal of working 160 hours per month is reasonable. Keep in mind that this doesn't include factors like him missing time from work due to being sick (unless he has paid sick leave).