The experimental primary school needs to buy a composition guidance book for each of the students in the fourth and fifth grades at a price of 15 yuan. It is known that there are 123 students in the fourth grade and 157 students in the fifth grade. How much is the total cost for two grades?
实验小学要为四、五年级的同学每人购买一本价格是15元的作文辅导书，已知四年级有学生123人，五年级有学生157人．两个年级一共需要多少钱？
<gadget id="calculator">123 + 157</gadget>
<output>280</output>

<gadget id="calculator">15 * 280</gadget>
<output>4_200</output>

<result>4_200</result>