How to solve for a max area given a set parameter?

I have a class problem which give us 30 one meter thick would panels. We are to write a program that allows us to build a rectangular yard to maximize area of said yard. Below is what I've come up with so far, however the problem I a having is that b and c (the length and width) are undetermined values. Is there a function in which i can set the 30 beams (a) equal to 2(b+c) (the parameter) where b and c together use a max of 30 beams (a)?

a=30;
b+c=a;
b=(a-2*c)/2;
a=2*b+2*c;
d=(b*c);
solve max a

Answer 1

[Walter Roberson]

You can use the symbolic toolbox. For example,

syms a b c
C = solve(b+c == 123,c)
a = b*C

now maximize a somehow

Answer 2

[Torsten]

Take a look at my answer under

http://www.mathworks.com/matlabcentral/answers/267427-how-can-you-maximize-area-of-a-rectangle-given-a-total-perimeter

Best wishes

Torsten.