b$)$ more $0$ s than $1s?$

c$)$ at least seven $1s?$

d$)$ at least three $1s?$

$21.$ How many permutations of the letters ABCDEFG contain

a$)$ the string $BCD?$

b$)$ the string CFGA $?$

c$)$ the strings $BA$ and $GF?$

d$)$ the strings ABC and $DE?$

e$)$ the strings ABC and CDE $?$

f$)$ the strings CBA and BED $?$