Actual area = (140-yd x 940-yd) = 131,600 square yards.
Estimated area = (100-yd x 850-yd) = 85,000 square yards
Error = (131,600 - 85,000) = 46,600 square yards
Error as a fraction of the actual area = 46,600 / 131,600 = 0.354...
To change a decimal to a percent,
move the decimal point 2 places that way ==> .
0.354... = 35.4.. % (rounded)