The -n option suppresses the automatic output of input lines (that's the default).
The p at the end tells sed to output the lines that matches.

This searches for lines at the left side of the division operator.
The characters within the brackets search for a numeric character or a variable and the space and asteric after the brackets for zero or more spaces.

This is the escaped division operator.

At the right side of the division operator we search for zero or more preceded spaces and a numeric character or a variable.

Regards