Question

solve this system using substitution
x=y
x-3y=4

Answer 1

solve for y or x for the second equation first

Answer 2

x-3y=4---> add 3y to both sides to solve for x
x=3y+4

Answer 3

now you have
x=y
x=3y+4
substitute the x, in other word equal them to one another

Answer 4

y=3y+4
solve for y

do the same for x