Given the systems of constraints, name all my the vertices of the feasible region. Then find the maximum value of the given objective function.

Constraints
X is greater than or equal to 0
Y is greater than or equal to 0
Y is less than or equal to 1/3x + 3
5 is greater than or equal to x+Y

Objective function: C=6x-4y

You have the two axes and two lines

I assume you can find the x- and y- intercepts of the lines.
The lines intersect where
1/3 x + 3 = 5-x
(3/2, 7/2)
Now you can evaluate C at the vertices.