If a+2b=30, what is the maximum product of a and b?
若a+2b=30，那么a、b乘积最大是多少．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">15 * (15/2)</gadget>
<output>225/2 = around 112.5</output>

<result>225/2 = around 112.5</result>