find the product of each of the following. state the non-permissible values

a) (7x2y5/x3)* (2xy2/21y)

b) -5a (6ab2/20b3c3)

c) (a+5/a+3) * (2a+6/4a)

d) (x-4/5x2-80) * (10x/x+1)