Free GMAT Practice Question

At a certain firm a sales agent is paid a fixed amount of $b$ dollars each month, plus a commission of $c$ percent of the amount by which her sales for that month exceed $t$ dollars. In one month her sales exceeded $t$ dollars and her total pay for the month was exactly twice her fixed amount. In terms of $b$, $c$, and $t$, what were her sales for that month, in dollars?