Eight times the difference of a number and seventeen is thirty"?

"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!

It will take him 5 days