Answer:
20
Step-by-step explanation:
Since we are told that line a is parallel to line b, even if it's not visible in the image, we can say that ∠5 = ∠1, since they are formed by the same line crossing parallel lines.
So, we have
∠4 = 3x
∠5 = ∠1 = 6x
Since ∠4 and ∠5 are complementary angles formed by line t, we know their sum is 180 degrees. So,
∠4 + ∠5 = 180
3x + 6x = 180
9x = 180
x = 20
Answer is 20.
