Question

If x can be any number, how many solutions are there for the equation?

Answer 1

C. There are many solutions
4(5)-1=19
4(10)-1=39

Answer 2

I agree...C is the answer.  Anytime you put in a value for X, you get a different Y answer, so yes, there are many answers.  The other answer gives you two examples using x = 5 and x = 10.  You could also substitute any other number for x and get a different y answer; an infinite number of x's and y's actually.