which of these is an example of a literal equation

A literal equation is one where we have several variables and we are trying to solve for one of them.....thus it's an "abstract" equation.....we are not trying to find a " numerical" answer

A is not an equation

C is an identity

D is a linear equation where we can find a numerical value for x 

B is the literal equation......we can solve for any variable [ either x or y ] in an abstract manner