If the weight of 40 kg is recorded as 0, then Xiao Liang's weight should be recorded as +3, and Xiao Ming's weight should be recorded as -6, so how much is the weight difference between Xiao Liang and Xiao Ming's weight in kilograms?
如果体重40千克记为0，那么小亮的体重应该记为+3，小明的体重应该记为-6，那么小亮和小明的体重相差多少千克．
<gadget id="calculator">3 - (-6)</gadget>
<output>9</output>

<result>9</result>