Marcus is having a water balloon party. He has 100 balloons. Each balloon holds 3 ounces of water. He can buy 50 ounces of water for $2.5 a bottle. If he walks into the store with 2 $10 bills, how much change will he have after he buys all the water he needs?
He will need 300 ounces of water because 100 x 3 = 
<gadget id="calculator">100*3</gadget>
<output>300</output>
300.
He will need 6 bottles because 300 / 50 = 
<gadget id="calculator">300/50</gadget>
<output>6</output>
6.
This will cost $15 because 6 x 2.5 = 
<gadget id="calculator">6*2.5</gadget>
<output>15</output>
15.
He has $20 because 2 x 10 = 
<gadget id="calculator">2*10</gadget>
<output>20</output>
20.
He will get $5 in change because 20 - 15 = 
<gadget id="calculator">20-15</gadget>
<output>5</output>
5.

<result>5</result>