To do this without leaving vi, you type:

You want to save vi changes to the file myfile with :w!, but vi complains it can not write to the file.
Therefore, you want to check the write permissions on the file. To do this without leaving vi, you type:

A.
:!ls -l myfile

B.
:\ls -l myfile

C.
esc :ls -l myfile

D.
:?ls -l myfile