p * q = 2p + pq + q

(p*2) - (p*1) = 40

firstly, p = p and q = 2, secondly p = p and q = 1

then, 2p + 2p + 2 - (2p + p + 1) = 40

4p + 2 - 3p - 1 = 40

p + 1 = 40

p = 40 - 1 = 39