He has sold (16+1/8) bushels/day x 7 days = (16 x 7) + (1/8 x 7) = 112 + 8/7 = 81 + 1/4 = 113.14
The change in the number of bushels is 120 - 113.14 = 6.857 or 6 and 857/1000 bushels
In other words, he has 58.75 (or 18 and 3/4) bushels remaining and has sold 81.25 (or 81 and 1/4) bushels
