How do you find the tax on a purchase and calculate the final bill? Give an example, then write and solve a number sentence to illustrate your strategy.

If you are buying something that cost $15 and sale tax is 6%, you can calculate final bill trough proportions:

$15:100%=$x:106%

100x=106*15, x = (106*15) / 100, x=$15.9 is final bill.

You can also use easier way: $15+0.06*$15=$15.9

Explanation for 2nd way: Cost is $15, on that you need to add 6% of $15: (6%/100%) * $15 and that is 0.06*15.