There are two types of TVs in the shopping mall, black and white TVs account for the total (2/5). After half of the black and white TVs and 15 color TVs are sold, the black and white TVs are color TVs (3/4). How many TVs are there in the shopping mall? (cannot be solved by equation)
商场有两种电视，黑白电视占总数的(2/5)，卖出一半黑白电视和15台彩电后，这时黑白电视是彩电的(3/4)，商场原有电视多少台？(不能用方程解)
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(2/5) / 2 / (3/4)</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">1 - (2/5) - (4/15)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">15 / (1/3)</gadget>
<output>45</output>

<result>45</result>