A woman owns a small, cash-only business in a state that requires her to charge 7% sales tax on each item she sells. At the beginning of the day, she has $210 in the cash register. At the end of the day, she has $1,173.00 in the register. How much money should she send to the state government for the sales tax she collected?
amount sold ... end of day minus beginning of day
she collects 1.07 times the marked price (that's the tax included)
tax collected ... amount sold * (.07 / 1.07)