Question 2637
Let Denis age be x
and Earl age be y

Sum of their ages is 42
=> x+y = 42..........equation(1)

Earl is 8 years younger then Denis
=> y = x -8............equation(2)

Substituting the value of y from equation(2) to equation(1)
=> x+y = 42
=> x + (x-8) = 42
=> 2x - 8 = 42
=> 2x = 42 +8
=> 2x = 50
=> x = 25
So Denis age is 25

Earl is 8 years younger then denis
SO Earl age = 25-8 = 17