Question

Find the value of x in x + y= 9 and x - y= 3.
6
-6
3
-3

Answer 1

x + y= 9 and x - y= 3

rearrange the second equation:

x - y= 3

x = 3 + y

x -3 = y

substitute y with "x-3" in the first equation and solve

x + y= 9

x + (x-3)= 9

2x -3 = 9

2x = 12

x = 6

you could also start with the first equation and substitute y in the second.

graphically speaking, it's the intersection point of to lines, at least the six-part of the point.