To solve a system of equations by substitution what is the best first step

Isolate one variable to one side.

Step-by-step explanation:

Example:

x+y = 8

2x+y=2

Then, take the second (or first, your choice) then isolate a variable:

2x+y=64 = y=2-2x

then plug the equation in:

x+2-2x=8

-3x=6

x=-2