Answer 7 & 10 for me and how to do i really need which is ironic since i learned this last year i was in 6 th grade now im in 7th and learning it again but guss i forgot

When subtracting a negitave number change it to a positive [1- -1=2] so 7 is 1 and 10 is 78 1/2

Whenever you subtract a negative, such as your example, 24 3/8 - - 54 1/8, you must change your negative into a positive. So the problem becomes 24 3/8 + 54 1/8. Add the mixed fractions together and you get 78 4/8. Don' forget to simplify! The answer will become 78 1/2.  Don't kill me if I'm wrong! 

Maybe the answer is 20mm. all i really did was just multiply, which is obvious.