Answer: (c) 35 is the correct option.
Step-by-step explanation: Given that triangles RST and XYZ are congruent to each other.
We are to find the value of x.
From the figure, we note that
RT = (x +21) units and XZ = (2x - 14) units.
Since RT and XZ are corresponding parts of the congruent triangles, so we must have

Thus, the value of x is 35.
Option (c) is CORRECT.