How many paying stones, each measuring 2 1/2 m * 2 m are required to pave a rectangular court yard 70 m long and 16 1/2 m board? Select:  A) 99  B) 18  C) 16  D) 10  E) 231

Rationale: "70 * 33 / 2 = 5 / 2 * 2 * x = > x = 231 answer : e"
Answer: E