An equation for a line in the xy-plane allows you to find the value of y, given x
the statement is true
here we are given with the value of x
so we have here two variables available
now it is a fact that if value of a variable is known in a equation we can easily get the value of other variable
here value of x is given which is a variable so it is evident that for a line in the xy-plane allows us to find the value of y, given x.