The student is wrong in not putting a parenthesis between 1/3 and x. An equation of a line has a general equation of y = mx + b where m is the slope and b is the y-intercept. In this case, most likely 1/3 is the slope and 0 is the y-intercept. However, writing the equation like that seems like the x variable is a denominator and if that is the case the equation will not represent a line already.