Question 178917
x+y=7
x-y=9

You must combine these equations into one equation by adding each side together:
x+y=7
x-y=9
_________

x+y+x-y = 16


Simplify:
2x=16
x=8


Now, you have a solution for one of the variables, x. Substitute this value for x into either of the original equations to solve for y.
8+y=7
y=-1


Now, you have the solution  x=8m y=-1. Substitute these values in to the original equations to confirm that they solve them both. They do.