What is the sum of all the proper fractions in which the fractional unit is (1/15).
在分数单位是(1/15)的真分数中，所有真分数的和是多少．
<gadget id="calculator">15 * 7</gadget>
<output>105</output>

<gadget id="calculator">105 / 15</gadget>
<output>7</output>

<result>7</result>