You have the following system of equations:
7x - y = - 1
-7x + 3y = -25
In order to solve the previous system, you can use different methods, as for example susbtitution or addition of equations.
In this case, you use the second one, due to the fact you have 7x in one equation and -7x in the other equation. In this way you can easily eliminate variable x and then solve for y. With the value of y you can replace it in any of the two equations and solve for x.
Summarizing, you proceed as follow:
- add up the given equations
7x - y = -1
-7x + 3y = -25
0 + 2y = - 26
- solve for y in the previous equation
2y = - 26
y = -26/2
y = -13
- replace the obtained value of y in one of the given equations, and solve for x
7x - y = -1
7x - (-13) = -1
7x + 13 = -1
7x = -1 - 13
7x = -14
x = -14/7
x = -2
Hence, the solution of the given system of equation is:
x = -2
y = -13