When a=3.2, b=2.4, c=1.5, what is the value of ab-ac.
当a=3.2，b=2.4，c=1.5时，ab-ac的值是多少．
<gadget id="calculator">2.4 - 1.5</gadget>
<output>0.9</output>

<gadget id="calculator">3.2 * 0.9</gadget>
<output>2.88</output>

<result>2.88</result>