How many strings of six lowercase letters from the English alphabet contain
Athe letter a?
Bthe letters a and b?
Cthe letters a and b in consecutive positions with a preceding b. with all the letters distinct?
Dthe letters a and b, where a is somewhere to the left of b in the string, with all the letters distinct?
Athe letter a?
Bthe letters a and b?
Cthe letters a and b in consecutive positions with a preceding b. with all the letters distinct?
Dthe letters a and b, where a is somewhere to the left of b in the string, with all the letters distinct?
