Correct answer gets brainliest Please explain as well 3x+5y=21 4x-2y = -24

x=-3 y=6

Step-by-step explanation:

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Trip uphill to the store:
distance = speed * time
               = (15mph)*(12minutes/60 minutes per hour)
               = (15mph)*(0.2 hours)
               = 3 miles

trip downhill back home is along the same path
so the trip downhill was also equal to 3 miles.

So the the entire trip was a distance of 6 miles
3 miles uphill and 3 miles downhill.

So the average speed = (15mph uphill + 30mph downhill)/2
                                    = 45 mph/2
                                    = 22.5 mpg

So the average speed of the entire trip uphill and downhill is 22.5 mph