Factor completely by grouping 3u^2+8u-3

3u^2+8u-3
with grouping, we have to find 2 numbers which add up to 8 and multiply to 3*(-3)= -9.
testing, we find that 9 and -1 add up to 8 and multiply to -9. 
so now we can write the original equation as 
3u^2-u+9u-3
you can factor the terms in pairs:
u(3u-1)+3(3u-1)=
(u+3)(3u-1)