A water tower that serves four neighborhoods around it holds 1200 barrels of water and is filled to the top each week. If one neighborhood uses 150 barrels of water in a week, the second neighborhood uses twice as many barrels of water as the first neighborhood in a week, and the third neighborhood uses one hundred more barrels of water than the second neighborhood in a week, how many barrels are left for the fourth neighborhood?
The second neighborhood uses 150 * 2 = 
<gadget id="calculator">150*2</gadget>
<output>300</output>
300 barrels of water.
The third neighborhood uses 300 + 100 = 
<gadget id="calculator">300+100</gadget>
<output>400</output>
400 barrels of water.
The first, second, and third neighborhoods together use 150 + 300 + 400 = 
<gadget id="calculator">150+300+400</gadget>
<output>850</output>
850 barrels of water.
Thus, the fourth neighborhood has 1200 - 850 = 
<gadget id="calculator">1200-850</gadget>
<output>350</output>
350 barrels of water left for it to use.

<result>350</result>