For a canal, the ratio of the completed to the unrepaired is 2:3. If another 30 meters are built, the ratio of the completed to the unrepaired is 4:1. How many meters is the total length of this canal?
一道水渠，已修的和未修的比是2：3，如果再修30米，已修的和未修的比是4：1，这条水渠全长多少米？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">2 + 3</gadget>
<output>5</output>

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

<gadget id="calculator">(4/5) - (2/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">30 / (2/5)</gadget>
<output>75</output>

<result>75</result>