Problem: a horse is tethered to one corner of a rectangular grassy field 36 m by 20 m with a rope 12 m long . over how much area of the field can it graze ?
Rationale: "area of the shaded portion = 1 ⁄ 4 × π × ( 12 ) 2 = 113 m 2 answer b"
annotated_formula: divide(multiply(power(12, const_2), const_pi), const_4)