Teacher Wang bought prizes for the students. A pair of triangles is 2.8 yuan, a pencil case is 5.6 yuan, and a pen is 2.7 yuan less than the total price of a pair of triangles and a pencil case. How much is a pen?
王老师给同学们买奖品．一副三角板2.8元，一个文具盒5.6元，一枝钢笔比一副三角板和一个文具盒的总价少2.7元．一枝钢笔多少元？
<gadget id="calculator">5.6 - 2.7</gadget>
<output>2.9</output>

<gadget id="calculator">2.8 + 2.9</gadget>
<output>5.7</output>

<result>5.7</result>