a triangle includes 3 angles summing up as 180°

so 180 = <p + <q+ <r -------- (1)

and here <p=80°

<q +<r=pq+pr

also pq=pr (given)

so, <q =<r = a ---------------- (2)

from (1) and (2)

<p +<q +<r =180°

80° + a + a =180°

2a = 180-80

a=100/2

a=50

so <p = <q =50°