Question 14061
let x = third number
    y = first number
    z = second number
We know x+y+z=6
also x = y+z (1).
and y = x+1  (2).
plug y back into equation (1) to get x = (x+1) + z.
Now subtract x from both sides of this equation to get
0=1+z.
Now subtract 1 from both sides to get
-1=z.
Now we know x=y+(-1), x+y+(-1)=6.
plug x into this equation to get
(y+(-1)) + y + (-1) = 6
solve for y.
we have,
y-1+y-1=6
2y-2=6
add 2 to both sides to get
2y=8
now divide by 2 to get
y=4

Now that we know z and y we can use equation (1) to find x.
x=4+(-1)= 3.

Hope this helps