No coding here just some ideas which you might need later.

In math.html you used round which is a method of the Math object.  There are others.  They allow you to:

All of these are structured much the same as round being methods which need the number inside the brackets.  The exception is pow which needs two numbers so looks like this:

var answer=pow(35,3);

That will multiple 35 by itself twice.  Feel free to try any of these if you think they might be useful for what you do.  Most Web developers will not need them though (and you can always look them up if you do need them later).