7/12.
Explanation:
Find a common denominator between 3/4 and 1/6. Since both 6 and 4 can go into 12, that will be our denominator.
With 1/6, you have to multiple 6 by 2 to get 12, so multiple 1/6 by 2/2 and you get 2/12.
For 3/4, 4×3=12, so do 3/4 × 3/3 and you get 9/12.
Finally, subtract John's value from Sandy's, or 9/12-2/12 and you get 7/12, so he ate 7/12 more than Sandy.
Hope this helps :)
