Simple,
look at the picture, you can tell it is an acute angle, or less than 90 degrees.
This being said, you know your answer has to be less than 90 (<90)
One line goes through 80, and the other goes through 20...
How to find the angle?
80-20=
=60
Now, is this number smaller than 90 as we stated earlier? It is, thus,
your answer is m<A=60 (B)