I need to know how to do this problem I am completely stuck

This is FACTORISATION.
To solve this problem we have to find the common terms in this equation.
Firstly, between the 5x³ and 10x² the like terms are 5. But the question is, where did the 5 come from? Well in Factorisation, we have to find the HCF between two terms. Here is my answer:
5x³+10x²-25x-50
5x²(1x+2)-25(x+2)-› HCF of 5 and 10 is 5, HCF of 25 and 50 is 25
(1x+2)(5x²-25)-› Add the numbers from the brackets and the numbers outside the brackets.
SO THE ANSWER IS (1x+2)(5x+25)
HOPE THIS HELPS!!!! ;)