When Xiaogang calculated 7*(a+4), he copied the formula into 7*a+4, which is much less than the correct result
小刚在计算7*(a+4)时，把算式抄成7*a+4，这样比正确的结果少多少
<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<gadget id="calculator">28 - 4</gadget>
<output>24</output>

<result>24</result>