Basically we do the math for the chance of each additional attack to happen, and we directly increase the damage.
EAC is the hardest to understand, since each additional chance is reduced by 50% each time an additional attack is successful.
So for 4 EAC, it’s a multiplier of 1 + (.5 + .25 + .125 + .0625)
For 4 MA it’s 1 + ( 4 * .5 )