A word problem is given, it is required to find the equation that models the situation.
Since Robin has 6 pairs and Rhonda borrowed x pairs, the expression for this can be written by subtracting x from 6:
[tex]6-x[/tex]
Note that this expression gives the number of pairs Robin will have left.
Since it is given that Robin had 4 pairs left, equate the expression to 4:
[tex]6-x=4[/tex]
Hence, the required expression is 6-x=4.
