Step One
Find RST
The two base angles are given as equal and one of the is 28. So is the other one.
SRT = 28
STR = 28
All triangles have interior angles that add up to 180 degrees.
RST + SRT + STR = 180
28 + 28 + RST = 180
56 + RST = 180 Subtract 56 from both sides.
RST = 180 - 56
RST = 124
Step two
Find the exterior angle
The exterior angle = Sum of the two remote interior angles (RST + SRT)
The exterior angle = 28 + 124
The exterior angle = 152
Step Three
Find the value of x
2*x = 152 Divide by 2
x = 152 / 2
x = 76
There is a quicker way of finding the exterior angle. I didn't see it until I had written step two.
The exterior angle + STR = 180 degrees. They are supplementary.
The exterior angle + 28 = 180
The exterior angle = 180 - 28
The exterior angle = 152