When a=7.8, b=4.4, c=5, what is the value of (ab)c.
当a=7.8，b=4.4，c=5时，(a-b)c的值是多少．
<gadget id="calculator">7.8 - 4.4</gadget>
<output>3.4</output>

<gadget id="calculator">3.4 * 5</gadget>
<output>17</output>

<result>17</result>