We know that in an isosceles triangle, the angles opposite the equal sides are equal.
Since ΔPQR is an isosceles with PQ = PR.
∴ ∠Q = ∠R = 70o
By the angle sum property, we have
∠P + ∠Q + ∠R = 180o
⇒ x + 70o + 70o = 180o
⇒ x + 140o = 180o
⇒ x = 180o − 140o
⇒ x = 40o