Question 61166
Please help me understand how to solve by substitution thank you, rob.

3X + y = -7
X - Y = -5
------------------------------------------------------------------------

substitution method:

take the second equation,

x - y = -5
bring  -y  to the right side

==> x = -5+ y
 now bring  -5  to the left side

==>  x + 5 = Y

 which gives the value of y as x+ 5

Now substitute the value of y in the first equation, 3x + y = -7

==> 3x + x + 5 = -7

==> 4x +5  = -7

subtract 5 from both sides of the equation 

==> 4x +5 -5  = -7 - 5

==> 4x  = -12

now divide both sides of the equation by 4

==> 4x/4  = -12/ 4

==>  x =  -3


Now substitute the value x = -3 in the first equation.

==>  3*-3  + y = -7

==>   -9+ y = -7

==>        y = -7 + 9

==>        y = 2

so the solution is 

x = -3 and

y = 2