Andrea needs 45 rhinestones to finish an art project. She bought a third of what she needed and found a fifth of what she needed in her supplies. How many rhinestones does she still need?
Andrea bought 45 / 3 = 
<gadget id="calculator">45/3</gadget>
<output>15</output>
15 rhinestones.
She found 45 / 5 = 
<gadget id="calculator">45/5</gadget>
<output>9</output>
9 rhinestones in her supplies.
Thus, Andrea still needs 45 - 15 - 9 = 
<gadget id="calculator">45-15-9</gadget>
<output>21</output>
21 rhinestones.

<result>21</result>