Question

3x + y = 17
4x - y = 18

Answer 1

3x+y=17
subtract 3x on both sides
y=17-3x
substitute 17-3x for y in the second equation
4x-(17-3x)=18
7x-17=18
7x=35
x=5

and now that you know x=5 you can plug that in to either of the original equations
3(5)+y=17
15+y=17
subtract 15 from both sides
y=2

Answer 2

The two equations given are
3x + y = 17 and 4x - y = 18
Now we will first take one equation
3x + y = 17
Then
y = 17 - 3x
Now replacing the value of y in the second equation we get
4x - y = 18
4x - (17 - 3x) = 18
4x + 3x - 17 = 18
7x = 35
x = 35/7
= 5
Putting the value of x in the first equation we get
3x + y = 17
(3 * 5) + y = 17
15 + y = 17
y = 17 - 15
y = 2
So the value of x is 5 and y is 2