COMMON EVENTS WUESTION

Hi I'm new here. I've stared making an RPG using RMXP and created a Common Event that starts after a monster has inploded dealing damage to the monster and the common event is set up deal a set amount of damage to the the players party regardless of defense. I was wondering if there was a way to make the damage dealt to the party be affective by each of the actors physical defense?

I currently have the base damage set to 100, I'm assuming I nedd to put this into a varible and then some how retrive each actors current defense and put each of those into a varible and then take the base damage and subtract the base defense and put each of those sums into a varible that returns the damage dealt onto the screen?