School tree planting. The third grade planted 45 trees, the fourth grade planted 15 more than the third grade, and the fifth grade planted twice as many as the fourth grade. How many more trees are planted in fifth grade than in third grade?
学校植树．三年级植了45棵，四年级比三年级多植15棵，五年级植的棵数等于四年级的2倍．五年级比三年级多植多少棵？
<gadget id="calculator">45 + 15</gadget>
<output>60</output>

<gadget id="calculator">60 * 2</gadget>
<output>120</output>

<gadget id="calculator">120 - 45</gadget>
<output>75</output>

<result>75</result>