The expression is .

                      (Commutative Property: a + b = b + a)

                  (Associative Property: (a + b) + c = a + (b + c))

                                 (Add: 4.25 + 8.25 = 12.5)

                                                (Add: 12.5 + 3.50 = 16)

The value of the expression is 16.