In the figure below, the two adjacent polygons are regular. What is the measure of ∠ABC?

Answer:
= 150°
Step-by-step explanation:
Since the polygons are regular, certain mathematical assumptions would help us here.
A square is a quadrilateral with all it's 4 sides equal and all it's angles equal.
Sum of angles of a regular quadrilateral = 360.
Therefore, a single angle = 360/4
= 90°.
The Triangle is adjacent to the side of the square. We will thus assume it's an Equilateral triangle.
For an equilateral triangle, all it's 3 angles = 180.
A single angle = 180/3
= 60°.
With this,
Angle ABC = 90° + 60=
= 150°