The answer is 784
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D= 5c
c is the number of customers and for every customer, Jenny earns d dollars.
Multiply the first equation by 2
2x + 2y =30
now we’ll add the second equation to the first equation
2x + 2y =30
-2x+5y= -2
7y=28
divide by 7
y=4
now plug y back into the first equation
x + 4 = 15
subtract 4
x=11
You find the area of one side of the cube which is 12.25 mm and multiply it by the number of side which is 6. and the answer is 73.5 mm