The experimental primary school needs to buy a composition guidance book for each of the students in the third and fourth grades at a price of 12 yuan. It is known that there are 155 students in the third grade and 145 students in the fourth grade. How much is the total cost for the two grades?
实验小学要为三、四年级的学生每人买一本价格为12元的作文辅导书．已知三年级有155人，四年级有145人，两个年级一共需要多少元？
<gadget id="calculator">145 + 155</gadget>
<output>300</output>

<gadget id="calculator">300 * 12</gadget>
<output>3_600</output>

<result>3_600</result>