Hello,

You generally have this equality :

But this is only if you know that 3x+5 indeed divides the polynom.

If you don't know, work by steps :

Study the term of highest degree :

This is 3x (-5x²)

So write it :

-5x²*5=-25x², so you have to add this term since you substracted it

Work the same way for 15x² = (3x)*5x

5x*5 = 25x

->

-->

Again, -12x=(3x)*(-4)

-4*5=-20

Here you go