Solution:
Let the bottle of sunscreen cost be $x. Then we can write
($x+ $6.50)+6%($x+ $6.50)=$16.43
Now solve this for x as below
[tex] ($x+ $6.50)+\frac{6}{100}($x+ $6.50)=$16.43\\ [/tex]
[tex] \frac{100x+650+6x+39}{100}=16.43\\ \\ 106x+689=1643\\ \\ 106x=1643-689\\ \\ 106x= 954\\ \\ x=9\\ [/tex]
Hence the bottle of sunscreen cost $9.