What, exactly, is your difficulty? Do you not know what any of those words mean?
To solve a pair of equation "by substitution" means to solve one equation for something and substitute that into the othe equation. Solve the equation for as a function of x (or ) and then substitute that into .
To solve a pair of equation "by elimination" means to algebraically combine the two equation to eliminate one of the unknowns. Here, I suggest that you subtract from eliminating y.
Finally, to solve a pair of equations "by graphing" means to do exactly that- graph both equations and see where the graphs intersect.
With each of those methods, I get 3 distinct solutions.