The relationship between you shoe size and the length of you foot l ( in inches) is given by s = 3l - 22 for men and s = 3l - 21 for women.
how long is your foot when your shoe size is the same as the length of your foot and you are the following gender>
a man :
a woman:

For the shoe size be equal to the length of the foot, this means that L must be equal to S. Now, since we have different equations depending on your gender, we first check the conditions for man.

Since S = 3L - 22 for men, for a person to have a foot length equal to his shoe size, we equate L to S as shown below.

L = S
L = 3L - 22
2L = 22
L = 11

Thus, we can see that men with 11-inch foot would have the same shoe size number. We can apply similar approach to find the length of a woman's foot that satisfies our conditions as shown.

L = S
L = 3L - 21
2L = 21
L = 10.5 

Hence, a woman with a 10.5-inch foot have 10.5 for a shoe size as well.

man: 11 inches
woman: 10.5 inches