Question 541036
Three numbers:  x, y, z.
y = 4x
x+z = 8
z = 8-x
.
x+y+z = 20
.
substitute
.
x +4x +8-x = 20
4x = 12
x = 3
y = 4*3 = 12
z = 8-3 = 5
.
Done.