It is known that a=5, b=0.4, c=21 what is the value of the formula 3a-6b+2c.
已知a=5，b=0.4，c=21式子3a-6b+2c的值是多少．
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<gadget id="calculator">6 * 0.4</gadget>
<output>2.4</output>

<gadget id="calculator">15 - 2.4</gadget>
<output>12.6</output>

<gadget id="calculator">2 * 21</gadget>
<output>42</output>

<gadget id="calculator">12.6 + 42</gadget>
<output>54.6</output>

<result>54.6</result>