It's a real simple formula:
1. If you have a fav in the parlay, divide it into 1 and then add 1... for example, with a -125 fav, do this (1/1.25) + 1 = 1.80
2. If have have an dog in the parlay, just add 1.... (fav is -180, 10 cent line, dog is +170).... so 1 + 1.70 = 2.70
3. Multiply the 2 of them together (or 3 for 4 teams) = 1.80 * 2.70 = 4.86
4. Subtract 1 (no matter how many teams in parlay) 4.86 - 1 = 3.86
5. That is how much you'd win for each unit you'd bet....
It looks hard, but is actually pretty easy....