It’s very easy.
You have to multiply the numbers like normal number (672x99) and after you have to add the point. Where? Count how many decimals there are, in this case there are 3 (6.72 = 2 decimals 9.9 = 1 decimal. 2+1 =3), so count 3 starting to right. 672x99=66528 = 66.528
I hope that you understand me because I’m not English so my English isn’t perfect.