walking 7 / 6 of his usual rate , a boy reaches his school 3 min early . find his usual time to reach the school ?
"speed ratio = 1 : 7 / 6 = 6 : 7 time ratio = 7 : 6 1 - - - - - - - - 7 3 - - - - - - - - - ? = 21 m answer : a"
multiply(3, 7)