Funny and amusing situations...

6*2 = 12 + 6*0.5 = 3 = 15, what kind of math knowledge is needed to calculate that? Even DaU can do it; if it really increases by 3, then 15*3, that would be really better than defense specialists.

I don't know why I'm writing this, but I'll try to explain.
Let's start with the fact that in elementary school, I was taught that increasing by 3 and in 3 are completely different things. What you wrote is 3 times, but in reality, it turns out to be 6 + 3 = 9.
Secondly.

6*2 = 12 + 6*0.5 = 3 = 15

This expression is just awful... At least the last part, 3 = 15...
If you're writing some kind of expression, please take the time to explain what the components mean? What is 6*2? What is 6*0.5?
And thirdly, are you familiar with the damage calculation formula in Heroes? Do you have a damage calculator? Have you tried calculating the damage with and without Stone Skin? Under LaBett and Tazar?