The school plans to divide the tree planting task between the sixth grade and other grades at a ratio of 5:3. As a result, the number of trees planted in the sixth grade accounted for 75% of the whole school, 20 more than planned. How many trees did the school plan to plant?
学校计划把植树任务按5：3分给六年级和其它年级．结果六年级植树的棵数占全校的75%，比计划多栽了20棵．学校原计划栽树多少棵？
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">5 + 3</gadget>
<output>8</output>

<gadget id="calculator">5 / 8</gadget>
<output>5/8 = around 0.625</output>

<gadget id="calculator">(3/4) - (5/8)</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">20 / (1/8)</gadget>
<output>160</output>

<result>160</result>