The school assigns the task of planting a batch of saplings to the sixth, fifth and fourth grades according to the ratio of 5:4:3, and the sixth grade is assigned 30 more saplings than the fourth grade. How many saplings are there in total?
学校把种植一批树苗的任务按5：4：3的比例分配给六、五、四三个年级，六年级比四年级多分配到30棵树苗．这批树苗共多少棵？
<gadget id="calculator">5 + 4 + 3</gadget>
<output>12</output>

<gadget id="calculator">5 / 12</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">3 / 12</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(5/12) - (1/4)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">30 / (1/6)</gadget>
<output>180</output>

<result>180</result>