The answer for the question is D!!
"The number" is first, do an example, to find out how, like pick any number under 17. Let's do 14. Their difference is 3. 8*3=24. that;s not quite 30. We have to find a number to equal 30, let's pick 15 and 17. Their difference is 2. 2*8=16. Not quite. Now, check the multiplication table for 8. Do any of them equal 30? No. So now you can see that the answer is going to have a decimal place. Divide 30 by 8. That equals to 3.75. Now do 17 minus 3.75. That is 13.25. The difference between 13.25 and 17 is 3.25. Now, do 8*3.75. That is 26. Oops. I am not in high school, but keep going like that and YOU'LL FIND IT! I BELIEVE IN YOU!
Wow lots to ask for here... give me 4min I got you