Serious help needed for easy questions

well ive been give a series of questions although ive forgotton the method to solve most of them ive managed to get them done through books and the internet, there is a few i couldnt get done. id be greatful if some1 would point me in the right direction.

a) evaluate 1-a/a-1 when a = x+y/x-y.

b) simpilify (2/x + 5/y / 8y/x - 20x/y)

c) i have 2 complex numbers z1 and z2, z1-z2 = 5

z1 = x + i/2 - i

and

z2 = y/3 + 2i

how would i go about finding x and y?

thanks very much