When you multiply the first factor(
a trinomial) with the binomial expansion, you can obtain terms in x only from the product of the 2nd term of the trinomial with the 1st (
the constant term) of the expansion and the product of the 3rd term of the trinomial with the 2nd term of the expansion, which added together gives you (2-30)x
"
how'd u do it so easily?": -
if you have as many years of practice as I have, you'd be able to do it just as easily.