Hello there! 
7x² - 13x - 24 
We wanna start by writing -13x as a sum or difference. So it should look like this:
7x² + 8x - 21x - 24 
For 7x² + 8x we need to factor out x 
x(7x + 8) - 21x - 24. 
Now factor out -3 for -21x - 24 
x(7x + 8) - 3(7x + 8) 
Now we can factor out 7x + 8 from the expression 
(7x + 8)(x - 3)
Let me know if you have any questions about the answer. As always, it is my pleasure to help students like you!