In your question you want -15.6/-4?
We can say that total number of guppies would simply be the sum of two polynomials.
To get our answers we need to add those two polynomials. We add polynomials by adding their like terms. Like terms are those that have the same exponent.

So the total amount of guppies would be modeled using this polynomial:
30 inches of ribbon because in one foot there are 12 inches so in 2 feet there are 24 inches. And 30 is greater than 24 so therefore 30 inches of ribbon is longer than 2 feet of ribbon
Your answer would be the second option, (3a - 4)(a + 3).
We can see that this is the correct answer as if we expand it using FOIL, we get 3a² + 5a - 12:
(3a × a) + (3a × 3) + (-4 × a) + (-4 × 3) = 3a² + 9a - 4a - 12
= 3a² + 5a - 12.
I hope this helps!