Simplify first and then evaluate: when a=0.3, find the value of 5a+8a-0.8.
先化简后求值：当a=0.3时，求5a+8a-0.8的值．
<gadget id="calculator">13 * 0.3</gadget>
<output>3.9</output>

<gadget id="calculator">3.9 - 0.8</gadget>
<output>3.1</output>

<result>3.1</result>