The answer to your question is <span>−10.8</span>
<h2>add 60+168+276+304 and you get 810 square inches then add 3+14+8 and equals 835.</h2>
Years of decay...
It takes around 4 years for something to go through their half life (depending on the thing). This chart is showing the years go by (half lives that occur within the years) while the decaying is happening.