\[\boxed{\mathbf{27}\mathbf{.}}\]
\[24 + 15 = 24 + 10 + 5 =\]
\[= 34 + 5 = 39\]
\[31 + 12 = 31 + 10 + 2 =\]
\[= 41 + 2 = 43\]
\[46 + 11 = 46 + 10 + 1 =\]
\[= 56 + 1 = 57\]
\[52 + 16 = 52 + 10 + 6 =\]
\[= 62 + 6 = 68\]
\[25 + 22 = 25 + 20 + 2 =\]
\[= 45 + 2 = 47\]
\[43 + 24 = 43 + 20 + 4 =\]
\[= 63 + 4 = 67\]
\[32 + 32 = 32 + 30 + 2 =\]
\[= 62 + 2 = 64\]
\[61 + 33 = 61 + 30 + 3 =\]
\[= 91 + 3 = 94\]
\[35 + 41 = 35 + 40 + 1 =\]
\[= 75 + 1 = 76\]
\[51 + 34 = 51 + 30 + 4 =\]
\[= 81 + 4 = 85\]
\[64 + 15 = 64 + 10 + 5 =\]
\[= 74 + 5 = 79\]
\[72 + 25 = 72 + 20 + 5 =\]
\[= 92 + 5 = 97\]