Factor each expression
1)4a^2-16ab^3+8ab^2c 2) n^2+8n+15
3) g^2-9g+20
4) z^2-7z-30
5) 4y^3-36y

 1 -since everything includes 4a, we can factor that to get 4a(a-4b^3+2b^2c)
2 - since 5 and 3 add to 8 and multiply to 15, we can do (n+5)(n+3)
3 - since -5 and -4 add to -9 and multiply to 20, we can do (g-5)(g-4)
4 - since -10 and 3 add to -7 and multiply to 30, we can do (z-10)(z+3)
5 - we can factor out 4y to get 4y(y^2-9). 

I got the numbers in 2, 3, and 4 with a guesstimating and checking approach

All you have to do is multiply