a rope of which a calf is tied is increased from 12 m to 21 m , how much additional grassy ground shall it graze ?
"π ( 212 – 122 ) = 933.4 answer : a"
multiply(subtract(power(21, const_2), power(const_10, const_2)), divide(add(multiply(12, const_2), const_2), add(const_4, const_3)))