So the ratio of boys to girls is 12:24.. now, is that an equivalent ratio as 2 boys for 4 girls? or 2:4? let's see.

you could start simplifying the 12/24 fraction by dividing by some common multiple, say 2, and get 6/12, then divide by 3 and get 2/4 and stop there.
then you'll notice that 12/24 is really 2/4 in disguise.
30.6 because 10.2 times 30 is 30.6
The Factor Theorem says (x - a) is a factor of function p(x) if p(a)=0
so check for p(-2)
= -2^4 +3(-2)^3 + 4(-2)^2 - 8
= 16 - 24 +16 -8
= 0
so (x + 2) is a factor