Yeah j as the subject and it is part of the fraction.can u be more specific about wat u want? did u want to make j the subject? also is j part of the fraction?
cross multiply and u get
Qp - Qj = sp
Qj = Qp - sp
j = (Qp - sp)/Q
(Q/P)=S/(P-J)Q/p = s/p-j
Q/p = s/(p-j)Q/p = s/p-j