Cost of 7 gallons=$24.50
Cost of 1 gallon=24.50/7=3.5
Cost of 15 gallons=15*3.5=52.5
Cost of 15 gallons will be $52.5
The answer is in the image
The total nom of code that can be used is equal to 5+3 = 8
The solution is in the following image
The solution is given in the image below
Let the father's age be x and son's be y
10 years before-
Father age=x-10
sons age=y-10
Given,
x-10=10(y-10)
x-10=10y-100
Given present age of father=40
therefore,
x=40
40-10=10y-100
10y-100=30
10y=130
y=130/10
y=13
Therefore present age of son=13years
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