The sports group has 13 volleyballs and 15 footballs. These balls are equivalent to (4/7) of the total number of school ball games. What is the total number of school ball games?
体育组有排球13个，足球15个，这些球相当于学校球类总数的(4/7)，学校球类总数是多少？
<gadget id="calculator">13 + 15</gadget>
<output>28</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">28 / (4/7)</gadget>
<output>49</output>

<result>49</result>