The answer is 98 yards.
Explanation:
The new width is 40 yds + 2 yds = 42 yds.
Area = L × W
4200 square yds = L × 42 yds
L = 4200 yds ÷ 42 yds = 100 yds
The new length is 100 yds.
The old length = the new length - the width of the path × 2 = 100 yds - 1 yd × 2 = 100 yds - 2 yds = 98 yds.