Answer:
The rate of sales tax in her state is 7.41%.
Explanation:
First, you need to determine the cost of the items:
(35*2)+40+18=70+40+18=$128
Now, you can find the difference between the total Cynthia owes at the register and the cost of the items:
$138.24-$128=$10.24
Finally, you can use a rule of three to determine the rate of sales tax given that 138.24 represents 100%:
138.24 → 100%
10.24 → x
x=(10.24*100)/138.24= 7.41%
According to this, the answer is that the rate of sales tax in her state is 7.41%.