To find the maximum profit we need to maximize the function.
First we need to find the critical points, to do this we need to find the derivative of the function:

now we equate it to zero and solve for x:

hence the critical point of the function is x=105/4.
The next step is to determine if the critical point is a maximum or a minimum, to do this we find the second derivative:

Since the second derivative is negative for all values of x (and specially for x=105/4) we conclude that the critical point is a maximum.
Hence the function has a maximum at x=105/4. To find the value of the maximum we plug the value of x to find y:

Therefore the maximum profit is $605