\[\boxed{\text{6.1}\text{2}\text{7.}}\]
\[\textbf{а)}\ 53,17 - (5,52 + 23,17) =\]
\[= (53,17 - 23,17) - 5,52 =\]
\[= 30 - 5,52 = 24,48\ \]
\[\textbf{б)}\ 261,4 + (24,6 + 2,22) =\]
\[= (261,4 + 24,6) + 2,22 =\]
\[= 286 + 2,22 = 288,22\ \]
\[= 90 + 0 = 90\]
\[= 47 + 28,66 = 75,66\]