simplify: -2(a-3b)-4a+7b
expand and simplify: 3(7x-2y)-5(2x+y), 4h(k-3h)-6k(h-9k), (5b-7)(3+6b), (7b+3)(5-2p)-(4-3p)(p-1)
factorise: a²+5a-6, 12a²-19d+5
factorise using identities of algebra:4k ²+12k+9,81a ²-49b ²