Sue and her sister buy a $2,100 car.  They agree to split the cost based on the percentage of days use.  Sue's sister will drive the car 4 days a week and Sue will get the rest of the days.  How much does Sue have to pay?
Sue will drive 7-4=
<gadget id="calculator">7-4</gadget>
<output>3</output>
3 days a week.
So she will pay 2100*3/7=$
<gadget id="calculator">2100*3/7</gadget>
<output>900</output>
900.

<result>900</result>