Answer:
C. 7.50 hrs
Step-by-step explanation:
Since it takes 90 mins to clean 11 windows, the rate that it takes the washer per window is [tex]\frac{90}{11}[/tex] minutes. At this rate, if he were to clean 55 windows it would take him [tex]\frac{90}{11}(55) = 450[/tex] minutes. This translates into 7.50 hrs.