This is a permutation since order matters. If you have a calculator that does statistics there is a button for this nPr. If not, look at it this way, you have three positions to fill, how many runners are there that could come in first place? 7, How many are left to come in second place? 6, How many are lady to come in third place? 5.
Multiply these numbers together to get your answer: 7 x 6 x 5 = 210