Find the first three terms of the arithmetic series
a1=-10, an=26 and sn=80

The value of x is 38°

Step-by-step explanation:

Given: ∠SRT ≅ ∠STR, m∠SRT = 28°, m∠STU = 4x

We are given ∠SRT = ∠STR

But ∠SRT = 28°

Therefore, ∠STR = 28°

Supplementary Angle: Sum of of two angles on straight line is 180°

∠STR + ∠STU = 180°

   28° +  4x     = 180°

                4x  = 180 - 28

                4x  = 152

                  x  = 38°

Hence, The value of x is 38°