Question

(p-1)q - (p-1)p

Plz factor.

Answer 1

(p-1)q-(p-1)p
take out the common factor (p-1) then you'll get
(p-1)(q-p)

If this is not clear, replace (p-1) with k, then
(p-1)q-(p-1)p
=kq-kp
=kq+k(-p)
=k(q-p)  
now substitute k=(p-1) to get
=(p-1)(q-p)