Bernie has 4 dogs. They each need a certain amount of exercise per day. The first needs to walk 1 mile. The second needs to walk 4 miles. The third needs to walk 3 miles. On average, they need to walk 3 miles per day. How many miles does the last dog need?
The total walk distance must be 12 miles because 4 x 3 = 
<gadget id="calculator">4*3</gadget>
<output>12</output>
12.
The first three walk a total of 8 miles because 1 + 4 + 3 = 
<gadget id="calculator">1+4+3</gadget>
<output>8</output>
8.
The last one needs 4 miles because 12 - 8 = 
<gadget id="calculator">12-8</gadget>
<output>4</output>
4.

<result>4</result>