\[\boxed{\mathbf{489}.}\]
\[1)\ (1,72 + 3,428) + 2,28 =\]
\[= (1,72 + 2,28) + 3,428 =\]
\[= 4 + 3,428 = 7,428\]
\[3)\ 28,964 + 51,17 + 48,036 =\]
\[= (28,964 + 48,036) + 51,17 =\]
\[= 77 + 51,17 = 128,17\]