what is 8 times the square root of 3

That's already a nice number because it can't be simplified any more, but if you want its decimal value, you can use the caculator on this site.

$${\mathtt{8}}{\mathtt{\,\times\,}}{\sqrt{{\mathtt{3}}}} = {\mathtt{13.856\: \!406\: \!460\: \!551\: \!018\: \!3}}$$