Answer:
x = 24
Explanation:
Since SR = ST then Δ RST is isosceles, thus the base angles are congruent.
∠ SRT = ∠ STR = 4x - 60
∠ STR and ∠ STU are adjacent and supplementary, thus
∠ STR + ∠ STU = 180, substitute values
4x - 60 + 6x = 180, that is
10x - 60 = 180 ( add 60 to both sides )
10x = 240 ( divide both sides by 10 )
x = 24