Some colorful dragonflies flew over the grass, among which red dragonflies accounted for (2/5). Later, 12 yellow dragonflies flew over. At this time, the ratio of red dragonflies to the total number of dragonflies was 1:4. How many red dragonflies are there?
草地上飞来了一些五颜六色的蜻蜓，其中红蜻蜓占(2/5)．后来又飞来了12只黄蜻蜓，这时红蜻蜓与蜻蜓总数的比是1：4．红蜻蜓有多少只？
<gadget id="calculator">4 / 1</gadget>
<output>4</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">4 - (5/2)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">12 / (3/2)</gadget>
<output>8</output>

<result>8</result>