A rectangular field is to be fenced on three sides leaving a side of 20 feet uncovered. If the area of the field is 10 sq. feet, how many feet of fencing will be required?
Choose the correct choice from the following options.
A) 34
B) 40
C) 68
D) 21
E) 78

Rationale: "we have : l = 20 ft and lb = 10 sq . ft . so , b = 0.5 ft . length of fencing = ( l + 2 b ) = ( 20 + 1 ) ft = 21 ft . answer : d"
Answer: D