This is called middle term splitting method in which firstly you need ti multiple the cofficients of x2 and constant.
In your question it would be24?3 which will equal to -72.
Now you have to find such two numbers which on adding give cofficient of x and on multiplying gives -72
In this question it would be-9 and 8 so on adding it we get -1 and on multiplying it we get-72
After it u just need to take common and equate with it 0
