3y × (2x — 1) — (xy — 1) — 5x × (y + 3) + 6 × (x + y + 10) =
6xy — 3y — xy + 1 — 5xy — 15x + 6x + 6y + 60 =
6xy — 5xy — xy — 3y + 6y — 15x + 6x + 1 + 60 =
6xy — 6xy + 3y — 9x + 61 = 3y — 9x + 61 =
3 × (y — 3x + 20) + 1.
2a × (3 — b) —3b × (2 — a — 5 × (ab — a — b)) =
6a — 2ab — 3b × (2 — a — 5ab + 5a + 5b) =
6a — 2ab — 3b × (2 — 5ab + 5b + 4a) =
6a — 2ab — 6b + 15ab² — 15b² — 12ab =
15ab² — 15b² — 12ab — 2ab + 6a — 6b =
15ab² — 15b² — 14ab + 6a — 6b =
15b² × (a — 1) + 6 × (a — b) — 14ab