Then 50 (Lucario's HP)-(40(Marth's Magic) +10 (Dancing Blades Strength))-20 (Lucario's Resistance)= 30 damage...from the first strike. In other words Marth dealt a total of 90 damage if my calculations are correct, feel free to correct them if they're not. Sorry this took so long, I had to do a lot of rifling.
EDIT: I'll take next.