Lets look at and example. Assume for a moment that
A=[a1, a2], B=[b1, b2] where each element is a real number.
Remember that matrix addition is done component wise.
Thus A+B = [a1, a2]+[b1, b2] = [a1+b1, a2+b2]
and B+A = [b1, b2]+[a1, a2] = [b1+a1, b2+a2]
so the question is, is a1+b1=b1+a1 and a2+b2=b2+a2
Remember the commutative property of addition.
Can you expand this example to fit your problem?