We'll group the first two terms of the sum and the last two term and we'll get:
`(28y^3 + 21y^2) + (36y + 27)`
We'll factor `7y^2` within the first pair of brackets and we'll factor 9 within the 2nd pair of brackets:
`7y^2(4y + 3) + 9(4y + 3)`
We notice the common factor (4y + 3):
`(4y + 3)(7y^2 + 9)`
Therefore, the factorised result is `(4y+3)(7y^2 + 9)` .