on the graph it show (2, 3) and (4, 1)
Without more information about the graph this is a tough question to answer. Given that the cost is C=3x+2y and we have two points to choose from, (2,3) and (4,1) we can work out a solution.
First recall that a point takes the form (x,y). So, (2,3) tells us that x=2 and y=3. If we plug those values into the equation for cost we see that C=3(2)+2(3) or C=6+6 or C=12. Thus the cost associated to point (2,3) is 12. Try to do the same sort of thing to find the cost at point (4,1), then compare those two numbers to find the point associated with the minimum cost.