Arthur has 3 dogs. They eat an average of 15 pounds of food a week. One dog eats 13 pounds a week. The second eats double this. How much does the third dog eat a week?
The second dog eats 26 pounds a week because 13 x 2 = 
<gadget id="calculator">13*2</gadget>
<output>26</output>
26.
In total they eat 45 pounds because 3 x 15 = 
<gadget id="calculator">3*15</gadget>
<output>45</output>
45.
The third dog eats 6 pounds a week because 45 - 13 - 26 = 
<gadget id="calculator">45-13-26</gadget>
<output>6</output>
6.

<result>6</result>