The sides of a rectangular field are in the ratio 3 : 4. If the area of the field is 8112 sq. m, the cost of fencing the field @ 25 paise per metre is  Pick one.
A) rs . 55.50  B) rs . 67.50  C) rs . 86.50  D) rs . 91.00  E) none of these

Rationale: "solution let length = ( 3 x ) metres and breadth = ( 4 x ) metres . then , 3 x × 4 x = 7600 ⇔ 12 x 2 = 8112 ⇔ x 2 = 676 ⇔ x = 26 so , length = 78 m and breadth = 104 m . perimeter = [ 2 ( 78 + 104 ) ] m = 364 m . ∴ cost of fencing = rs . ( 0.25 × 364 ) = rs . 91 . answer d"
Answer: D