Respuesta :

(7/b)-36=(28/b)
(7/b)-(28/b)=36
7-28=36b
-21=36b
-21/36=b

Therefore:
28/b=a/72
28/(-21/36)=a/72
28 * (36/-21)=a/72
-48=a/72
72* -48 = a
a=-3456

a=-3456
b=-21/36