Tropical Storm Sally brings 3 days of rain to southern Texas.  The first day it rained 4 inches.  The second day it rained 5 times as much as the first day, and the third day it rained 6 inches less than the sum of the first two days.  How much did it rain on the third day?
First Day:
<gadget id="calculator">4</gadget>
<output>4</output>
4 inches.
Second Day: 5(4)=20 inches.
Third Day: (4+20)-6=
<gadget id="calculator">(4+20)-6</gadget>
<output>18</output>
18 inches.

<result>18</result>