Lets take the info already given. 20 is on the larger triangle and 8 is on the smaller. So the side that matches with X is 6. The relationship between 20 and 8 is 2.5. How? 20/8=2.5. then you divide 6 by 2.5. That equals 2.4. So x=2.4. Hope that helps !
48 books divided by 7 books per box. So since 7 can go into 48 6 times to make 42, the remainder is 6 books are left out. 6 boxes are filled. I interpreted the remainder by subtracting 42 from 48. And that's all I did. :)
I hope you like this answer and have a good night! :D