Answer:
x = 14
Step-by-step explanation:
See the diagram of the triangle attached.
We have Δ RST where, ∠ RST = 7x -54 and ∠ SRT = ∠ STR {Since, given that, RS = ST}
Now, if ∠ STU = 8x, then ∠ STR = 180 - 8x {Since, ∠ STU and ∠ STR are supplementary}
So, ∠ SRT = ∠ STR = 180 - 8x
Now, from Δ SRT, ∠ RST + ∠ SRT + ∠ STR = 180
⇒ 7x - 54 + 180 - 8x + 180 - 8x = 180
⇒ 9x = 126
⇒ x = 14 (Answer)
