Here, ∠PRQ and ∠PRT are angles in a linear pair.

m∠PRQ + m∠PRT = 180°

∴70 + m∠PRT = 180

∴m∠PRT = 180 – 70

∴m∠PRT = 110°

Now, ∠PRT is the exterior angle of ∆PQR.

∴m∠P + m∠Q

= m∠PRT

∴m∠P + m∠P = m∠PRT ….(The measures of ∠P and ∠Q is same)

∴2m∠P = 110

∴m∠P = 110/2

∴m∠P = 55°