Question

If a and b are parallel lines, and m∠3 = 128°, what is the measure of ∠8?

Answer 1

The answer lies in <5. If you know how to get <5, you can get <8, since they're angles opposite each other.

Answer 2

Perhaps this site can teach you a little about it: http://www.mathopenref.com/anglestransinterior.html

Answer 3

134?

Answer 4

May I ask how you got 134? :O

Answer 5

<3 + <5 = 180°

Since you know the measurement for <3 already, you can solve the equation.

128°+<5=180°
<5= 180°-128°

Answer 6

nice work @monokerous