The area of a rectangular plot is 21 times its breadth. If the difference between the length and the breadth is 10 metres, what is its breadth?  Choose the correct answer
A) 10 metres B) 5 metres C) 11 metres D) data inadequate E) none of these

Rationale: "l × b = 21 × b ∴ l = 21 m and l – b = 10 ∴ b = 21 – 10 = 11 m answer c"
Answer: C