СЕ — биссектриса ΔKCT, значит ∠KCE = ∠ECT.
∠KCT = ∠KCE + ∠ECT.
Так как ∠KCE = ∠ECT, то ∠KCT = 2 * ∠ECT, тогда ∠ECT = ∠KCT / 2.
∠ECT = 100° / 2 = 50°.
x = ∠ECT = 50°.