The first step of solving a system of equations is to solve one equation for a variable. I'll solve the first one for y.
2x + y = 7 Subtract 2x from both sides
y = -2x + 7
Now, plug that y value into the y of the second equation and solve for x.
5x + y = 9 Substitute
5x + (-2x + 7) = 9 Adjust the signs to get rid of parentheses
5x - 2x + 7 = 9 Combine like terms
3x + 7 = 9 Subtract 7 from both sides
3x = 2 Divide both sides by 3
x =

Now, plug that into the first equation.
2x + y = 7 Substitute
2(

) + y = 7 Multiply

+ y = 7 Subtract

from each side
y = 5

The answer to the system of equations is
(
, 5
).