The transport team transported a batch of building materials to the construction site. On the first day, what was transported was 15 tons less than 30% of the total, on the second day it was 20 tons more than 40% of the total, and on the third day the last 49 tons were transported. How many tons are there in total for this batch of building materials?
运输队向工地运送一批建筑材料，第一天运的比总数的30%少15吨，第二天运的比总数的40%多20吨，第三天运完了最后的49吨．这批建筑材料共有多少吨？
<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<gadget id="calculator">49 + 5</gadget>
<output>54</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (3/10) - (2/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">54 / (3/10)</gadget>
<output>180</output>

<result>180</result>