Answer:
17.8 hours
Explanation:
Serena's bonus on $1200 sales is 15%×$1200 = $180. In order to make $500 for the week, then she must have at least ...
$500 - 180 = $320
in hourly pay.
At $18 per hour, that requires she work $320/($18/h) = 17.77_7 h.
Serena must work a minimum of about 17.8 hours to make $500.
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Comment on the answer
The exact result of the computation is 17 7/9 hours. Many payroll departments record hours to the nearest 1/4 or 1/10 hour. For Serena's pay to be at least $500, she must work 17.8 (rounded to tenths) or 18.0 (rounded to quarters) hours.