Hello! So, this question is in the form of ax² - bx - c. First thingd first, let's multiply a and c together. c = -8 and a = 5. -8 * 5 is -40. Now, let's find two factors that have a product of 40, but a sum of 18. If you list the factors, you see that 2 and 20 have a product of 40, but 2 - 20 is -18. The factors we will use are -2 and 20.
How to factor it:
For this question, you can use something called a box method and factor it by finding a factor of each column and row. Just make 4 boxes and put 5x² on the top left and -40 on the bottom left box. Put 2x on the top right box and -20x on the bottom left box. Now, factor out for each row and column. The factors should be 5x + 2 for the top part and x - 4 for the side. It should look like (5x + 2)(x - 4). Let's check it. Solve it by using the FOIL method and you get 5x² - 20x + 2x - 8. Combine like terms and you get 5x² - 18x - 8. There. The answer is B: (5x + 2)(x - 4)
Note: The box method may be challenging at first, but it can be really helpful on problems like these.