Is 3 and 9 a solution for y equals 4x-3?

Answer 1

x = 3, y = 9 is one solution from infinite number of solutions.

to find another solution just choose any number for x, substitue it in the equation, for example if x = 1, y= 4 * 1 - 3 = 1, so 1 and 1 is another solution for y = 4 x - 3

In this question there is only one equation which contains two variables, so there is no unique solution.

we need other independent equation contains the variables x and y then we can solve these equations simultaneously, i.e. we can find finite number of solution (its one solution in linear equations)