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Darius is X years old.
Jack is (X+87) years old.
11 years ago, Jack was (X+87-11) = (X+76) years old.
11 years ago, Darius was (X-11) years old.
The equation is
X+76 = 4*(X-11).
Solve it to get the answer : Darius is 40 years old now.
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Additions
(a) Then Jack's age is 40 + 87 = 127 years now.
(b) CHECK: 11 years ago Darius was 40-11 = 29 years old; Jack was 127 - 11 = 116 years old; = 4,
so the condition is satisfied and the solution is correct.
Is it realistic/likelihood or not - it was not asked in the problem, so I do not touch it . . .
Formally, my solution is correct.