Two classes in the sixth grade carried out tree planting activities, when Class 1 planted (1/4) of the total. It is found that 4 trees have been planted in class 2. At this time, the ratio of the number of remaining trees to the number of planted trees is 7:8. How many saplings are there in this batch?
六年级两个班开展植树活动，当1班种了总数的(1/4)时．发现2班已经多种了4棵，这时剩下的棵数与已种的棵数比是7：8，这批树苗多少棵？
<gadget id="calculator">7 + 8</gadget>
<output>15</output>

<gadget id="calculator">8 / 15</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(8/15) - (1/4) - (1/4)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">4 / (1/30)</gadget>
<output>120</output>

<result>120</result>