sandy is younger than molly by 12 years . if the ratio of their ages is 7 : 9 , how old is sandy ?
let sandy ' s age be 7 x and let molly ' s age be 9 x . 9 x - 7 x = 12 x = 6 sandy is 42 years old . the answer is a .
multiply(divide(7, subtract(9, 7)), 12)