Well first you have to turn the mixed number into a improper fraction.
7 2/8=59 over 8
2 7/9=25 over 9
Then u would multiply the 59 by 9 and 8 by 9 and u should get 531 over 72 and for the second fraction u should multiply the 25 by 8 and the 9 by 8 and you should get 200 over 72 as a improper fraction.
Then you have to subtract 531 over 72 by 200 over 72 and u should get 231 over 72 which is 4 and 43 over 72 when simplified.
The answer: 4 43/72
Hope this helps!!!!