sed command only please Linux, Redhat, unix

file I am working with: lines

cat lines

This is line 1. Line 2 line number 3 This is 4 Another line: 5 6 6 6 6 Line 7 eight 9 line ten

questions :

Delete all lines that don't have a number in it

Delete all lines that have a number in it

Change all words 'line' to 'LINE' and print all lines

Change all words 'line' to 'LINE' but print only the lines that are changed

print all lines but add a line of +++++ before and after each line