Part A
From the characteristics of triangles is that their angles always add up to 180 degrees. Also, angles 2 and 3 add up to 180 degrees as well since they combine to make a straight angle. We can use this knowledge to solve this problem.
First, we will find the measure of angle 2. Then, we will subtract that from 180, and the answer will be the measure of angle 3.
We will focus on triangle DEF.
In angle D, that little square shape means it is a 90 degree angle. We also know from the question that angle 1 is 53 degrees. So, to find angle 2, do 180-90-53=37. Angle 2 is 37 degrees.
So, angle 3 is equal to 180-37=143 degrees.
As for Part B:
In an isoceles triangle two angles are equal, and the third angle is different.
For triangle DEF, we have already found all three angle measures while doing part A. Angle 1 is 53 degrees, angle 2 is 37 degrees, and angle D is 90 degrees. So, this is not an isoceles triangle because no two angles are equal.