Answer: a. a literal equation
Step-by-step explanation:
A literal equation is an equation which comprises basically of letters., where letters are nothing but variables.
All the kinds of formulas are said to be examples of literal equations.
For example slope intercept form
The rate of change of position on a straight line , where 'd' is the distance and 't' is the time.
Therefore, a literal equation is an equation with more than one variables.