There are 120 students in the third grade of Hongguang Primary School, and the number of students in the fourth grade is twice that of the third grade. How many students are there in the third and fourth grades?
红光小学三年级有学生120人，四年级学生人数是三年级的2倍，三、四年级共有有学生多少人？
<gadget id="calculator">120 * 2</gadget>
<output>240</output>

<gadget id="calculator">240 + 120</gadget>
<output>360</output>

<result>360</result>