T-90. SERIOUSLY. STOP VANDALING. 

It is nothing no do with Ad Homenim. The problem is that you are not good at math at all, so you can not understand the basic equation; 550 + 250 = 800. 550 for T-90A Basic Armor, and 250mm for Kontakt5. So if T-90A equips the K5 ERA => That's 800mm. Do you even know what Kontakt5 is and how Explosive Reactive Armor works?