\[\boxed{\mathbf{48.}}\]
\[\textbf{а)}\ 42 + 30 = 72\]
\[6 + 31 = 37\]
\[25 + 14 = 39\]
\[4 + 50 = 54\]
\[65 - 23 = 42\]
\[77 - 5 = 72\]
\[60 - 18 = 42\]
\[100 - 4 = 96\]
\[\textbf{б)}\ 6 + 90 - 46 = 96 - 46 = 50\]
\[40 - 27 + 51 = 13 + 51 = 64\]
\[100 - 1 - 76 = 99 - 76 = 23\]
\[3 + 97 - 14 = 100 - 14 = 86\]
\[87 - (24 + 26) = 87 - 50 = 37\]
\[31 + (100 - 55) = 31 + 45 =\]
\[= 76\]
\[(90 - 8) + 18 = 82 + 18 = 100\]
\[70 - (100 - 39) = 70 - 61 = 9\]