Evaluation: When a=4 and b=0.4 are known, find the value of 5a-b**2.
求值：已知a=4，b=0.4时，求5a-b**2的值．
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">0.4 * 0.4</gadget>
<output>0.16</output>

<gadget id="calculator">20 - 0.16</gadget>
<output>19.84</output>

<result>19.84</result>