Isso fará o trabalho
awk '
/^[[:blank:]]*$/{for (k in a) print k, a[k]; delete a; print ""; next}
/:/{print; next}
{a[$1] += $2}
END {for (k in a) print k, a[k]}
' data
1: 6.1703
44 55.9
46 22.2
2: 6.1932
44 26.8319
46 24.42
3: 16.5
45 41.1
46 31