Tara's taking a road trip for the weekend.  She drives for two days, stopping to fill up her gas tank each time from empty to full when she needs it.  She visits 4 different gas stations in total, with the price of gas being $3, $3.50, $4, and $4.50 respectively at each.  If Tara's car has a 12-gallon tank, how much does she spend on gas for her road trip?
The first station Tara stops at charges $3 for a gallon of gas, so for her 12-gallon tank she spends 12*3= 
<gadget id="calculator">12*3</gadget>
<output>36</output>
36 dollars.
The second station Tara stops at charges $3.50 for a gallon of gas, so for her 12-gallon tank she spends 12*3.5= 
<gadget id="calculator">12*3.5</gadget>
<output>42</output>
42 dollars.
The third station Tara stops at charges $4 for a gallon of gas, so for her 12-gallon tank she spends 12*4= 
<gadget id="calculator">12*4</gadget>
<output>48</output>
48 dollars.
The fourth station Tara stops at charges $4.50 for a gallon of gas, so for her 12-gallon tank she spends 12*4.5= 
<gadget id="calculator">12*4.5</gadget>
<output>54</output>
54 dollars.
Now that we know all the individual amounts, we add 36+42+48+54= 
<gadget id="calculator">36+42+48+54</gadget>
<output>180</output>
180 dollars in gas in total.

<result>180</result>