The students planted trees, and 45 were planted in the fourth grade. Sixth graders planted 15 fewer plants than fourth graders. How many trees are planted in two grades?
同学们栽树，四年级栽了45棵．六年级栽的比四年级的2倍少15棵．两个年级共栽树多少棵？
<gadget id="calculator">45 * 2</gadget>
<output>90</output>

<gadget id="calculator">90 - 15</gadget>
<output>75</output>

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

<result>120</result>