x = 1st number, y = 2nd number, z = 3rd number
x + y + z = 26
y = 2x
z = 2x + 6
x + (2x) + (2x + 6) = 26
5x + 6 = 26
5x = 26 - 6
5x = 20
x = 20/5
x = 4 <=== first number
y = 2x....y = 2(4) = 8 <=== second number
z = 2x + 6....z = 2(4) + 6 = 8 + 6 = 14 <=== third number
