IMAS 2021–2022 Junior — Round 1 Question 8

Question 8

As show in the diagram below, we use some number of pentagons, that is identical to $ABCDE$ to fill the plane below. What is the angle measure, in degrees, of $\angle ABC$?

Question illustration

$100^\circ$
$105^\circ$
$120^\circ$
$135^\circ$
$150^\circ$