When a=2.5, b=1.8, c=1.4, what is the value of ab-ac.
当a=2.5，b=1.8，c=1.4时，ab-ac的值是多少．
<gadget id="calculator">1.8 - 1.4</gadget>
<output>0.4</output>

<gadget id="calculator">2.5 * 0.4</gadget>
<output>1</output>

<result>1</result>