K+l+m=l+m+k what property does this demonstrate

K + L + M = L + M + K is an example of Commutative Property of Addition

Commutative Property of Addition means the order of the terms doesn't matter. You can still get the same answer on both sides of the equation even though the order of numbers are not the same.

Example:
       5 + 3 + 7 = 3 + 7 + 5
                 15 = 15

As you can see above, the sum of the left side of the equation is the same as the sum of the right side of the equation which is 15.