So we multiply the denominator by 3n^3 to get this over here we also have to multiply the numerator by 3n^3 3n^3 times 6m is 18m, one right over there and then we have an n^3 now let's do it with the second term right over here or the thing we are subtracting from this first rational expression so to get from 3m, so let's see, to get from that to that what did we have to do? to get from a 3 to a 21 you have to multiply it by a 7 you have to multiply it by 7 and to get from an m to an m^2 you have to multiply it by m