Simple Addition

The concept of this application is very simple, it simply adds three numbers together and gives you the answer. This is the first app I have developed, so I don't know all the in's and out's. There are no ads due to the goal of this app being strictly educational. I intend on maybe developing this into something far more complex and more useful at a later time. As of the time being though I am just releasing this to better understand how designing/coding/releasing an app actually works. I tested this on many devices but for obvious reasons I couldn't test them all. Feedback is greatly appreciated!