(1 point) Consider the function f(x, y) = 3x+5y. List all critical points of f(x, y). If there are none, enter "none". If there is more than one, enter a comma-separated list of ordered pairs, e.g., "(1,2), (3,4), (5,6)". Critical points are List all critical points of f(x, y) which are local maxima. If there are none, enter "none". If there is more than one, enter a comma-separated list of ordered pairs, e.g., "(1,2), (3,4), (5,6)". Local maxima occur at List all critical points of f(x, y) which are local minima. If there are none, enter "none". If there is more than one, enter a comma-separated list of ordered pairs, e.g., "(1,2), (3,4), (5,6) ". Local minima occur at List all critical points of f(x, y) which are saddle points. If there are none, enter "none". If there is more than one, enter a comma-separated list of ordered pairs, e.g., "(1,2), (3,4), (5,6) ". Saddle points occur at