The function f(x) is shown on the graph. On a coordinate plane, a curved line shaped like a w, labeled f of x, crosses the x-axis at (negative 2, 0), (negative 1, 0), crosses the y-axis at (0, 12), and crosses the x-axis at (2, 0) and (3, 0).

What is f(0)?

check above link.

graphically?   well, you graph them both, the solutions is where they both intersect each other, since there are two solutions, meaning they will meet twice, or namely the linear will run into the quadratic curve twice, and where they meet, those x,y coordinates are the solutions to the system.