Hi Andya, ------------ x + y = 11 That means x = 11- y now: X 8 y = 30 install instead of x it's equivalent (11-y) you get: (11 - y) * y = 30 --------- gives you -y^2 + 11y = 30 Set it nicer: y^2 - 11y + 30 = 0 -------------- y^2 - 6y - 5y + 30 = 0 ---------- y * (y - 6) - 5 * (y - 6 ...