Question 246821
when we solve by substitution we solve one of the equations for x or y and then substitute that in the other equation
so if we solve 2x-y=4 for y, we will put the result in 2x-y=3  for y.
let's solve for y
2x-y=4
add y to both sides
2x=4+y
subtract 4 from both sides
2x-4=y
now substitute 2x-4 for y in 2x-1y=3 
2x-1(2x-4)=3
Be careful of the signs
minus a plus is minus 
but minus a minus is plus
if there is no sign it is a plus