!! used as default html header if there is none in the selected theme.
The server will give you the graph of two functions f (x) and g(x), whose expressions will be hidden. You will then be presented a certain number of other graphs, corresponding to functions such as f (x)+g(x), f (-x)-g(x), -f (x)+g(-x), etc (see the menu below). And you should locate the one which corresponds to one which will be precised in a question. To give the reply, you can simply click on the graph which you believe to be the good one.