Question

Substitution - add/subtraction method for 2 equations:

x + 3y = 19
x - y = -1

Answer 1

First, just isolate one of the variables, Let's isolate (x):

x - y = -1

-y = -1 - x

y = 1 + x

now lets plug in the (y) into the other equation:

x + 3y = 19

x + 3(1 + x) = 19

x + 3 + 3x = 19

4x + 3 = 19

4x = 16

x = 4

now lets use this to find our (y)

y = 1 + x

y = 1 + 4
y = 5

so x = 4, y = 5