Differentiating a bilinear function with the symbolic Toolbox

Assume we have functions, which look like this:

a(x,y) = 1 + 2x + 3y + 4xy

b(x,y) = 5 - 6x + 7y - 8xy

can I somehow get the result of the differentiation of y with respect to a?

Or the differentiation of x with respect to a?

Or the differentiation of y with respect to b?

Or the differentiation of x with respect to b?...