Students in grades five and six will plant trees, with an average of 90 trees in each grade, and the simplest integer ratio for tree planting in grades three is 2:3:4. How many more trees are planted in sixth grade than in fourth grade?
五、六年级同学去植树，平均每个年级植树90棵，三个年级植树的最简整数比是2：3：4．六年级比四年级多植树多少棵？
<gadget id="calculator">2 + 3 + 4</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">2 / 9</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">(4/9) - (2/9)</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">90 * 3 * (2/9)</gadget>
<output>60</output>

<result>60</result>