The sum of (21/5) times of a number and its (14/5) times is equal to 49, find this number.
一个数的(21/5)倍与它的(14/5)倍的和等于49，求这个数．
<gadget id="calculator">21 / 5</gadget>
<output>21/5 = around 4.2</output>

<gadget id="calculator">14 / 5</gadget>
<output>14/5 = around 2.8</output>

<gadget id="calculator">(21/5) + (14/5)</gadget>
<output>7</output>

<gadget id="calculator">49 / 7</gadget>
<output>7</output>

<result>7</result>