Matlab help writting an equation

I don't understand what is wrong with this equation:

Z=(n*R*y/(x-b))-((n.^2)*a)/(x.^2)

Matlab keeps telling me:

??? Error using ==> mrdivide

Matrix dimensions must agree.

Error in ==> g261x05 at 11

Z=(n*R*y/(x-b))-((n.^2)*a)/(x.^2)

when I try and run:

n=1.5; a=1.39; b=0.03913; R=0.08206

y=[273:.1:473];

x=[.3:.1:1.2];

[X,Y]=meshgrid(x,y);

Z=(n*R*y/(x-b))-((n.^2)*a)/(x.^2)

surf(X,Y,Z)

xlabel('Volume (L)');

ylabel('Temperature (K)');

zlabel('Pressure (atm)')

Please help!

It's g285x07 in Gilat if you have the book.

Thanks