The school assigns the tree planting task to the fourth and fifth grades at a ratio of 3:5. The fifth grade planted 108 trees, exceeding the original assignment (1/5). How many trees should the fourth grade plant?
学校把植树任务按3：5分配给四、五两个年级．五年级栽了108棵，超过了原分配任务的(1/5)，四年级原来要植树多少棵？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">108 / (6/5)</gadget>
<output>90</output>

<gadget id="calculator">90 / 5</gadget>
<output>18</output>

<gadget id="calculator">18 * 3</gadget>
<output>54</output>

<result>54</result>