Answer: The measure of angle 8 is 123° .
Explanation:
Since we have given that
m∠7 = 57°
we have two lines intersecting each other at one point forming angles ∠7, ∠8, ∠5, ∠6.
So, Relation between ∠7 and ∠8 is linear pair.
And we know that ,

Hence, the measure of angle 8 is 123° .