2x+y=10
y=5x-11
solve the system of equations by substitution

2x+5x-11=10!
So once you combine like terms - 2x+5x, you end up with 7x-11=10
You then have to add 11 to both sides of the equal sign and you get 7x=21. If you divide both sides by 7, you end up with x=3.
Did you need what Y was, too ? If so, you just go back to the original problem:
2(3)+y=10
2 times 3 = 6+y=10.
Subtract 6 from both sides and you get Y=4!

Don’t worry about it