Answer:
40
Explanation:
First let x represent the first number.
Let 2x represent the second number.
Let 2x-16 represent the third number.
x + 2x + 2x-16 = 84
5x -16 = 84
5x = 84 + 16
5x = 100
Divide both sides of the equation by 5 so that x can stand alone.

x = 20
∴ First number = x = 20
Second number = 2x = 40
Third number = 2x - 16 = 24