Let y reperent the other number
from the first information,
y = 2x -8 _____ (1)
from the second information,
x + y = 40 _____(2)
substituting the value of y = 2x-8 in equation (1) into equation (2), we have
x + y = 40
x + 2x - 8 = 40
3x -8 = 40
3x = 40+ 8
3x = 48
x = 48/3
x = 16