There are 3 classes in the fourth grade, with 50 students in each class, including 70 girls. How many boys are there?
四年级有3个班，每班50个人，其中女生有70人．男生有多少人？
<gadget id="calculator">50 * 3</gadget>
<output>150</output>

<gadget id="calculator">150 - 70</gadget>
<output>80</output>

<result>80</result>