You can do this problem in two ways. Either the long way or the short and easy way.
Here is the easy way:
You do 180x1.06 to get you their total of $190.80
Or you can do the slightly longer way which finds you the tax amount which then you can add onto the total:
You do 180*0.06 which gets you $10.80 of tax. $10.80 is how much tax they have to pay on top of the $180, then we can do 180+10.80 to get us the grand total of $190.80.