Sarah has a rope that is 20 meters long. Her friend wants to buy the rope for $2 a meter. Sarah plans to use the profit to buy a new rope, which at the store costs $1.5 a meter. How much money will she have left over after she buys the new rope?
Her friend pays her $40 for the rope because 20 x 2 = 
<gadget id="calculator">20*2</gadget>
<output>40</output>
40.
She can buy the rope at the store for $30 because 20 x 1.5 = 
<gadget id="calculator">20*1.5</gadget>
<output>30</output>
30.
She has $10 left over because 40 - 30 = 
<gadget id="calculator">40-30</gadget>
<output>10</output>
10.

<result>10</result>