Answer:
x = 4
Explanation:
An exterior angle of a triangle is equal to the sum of the remote interior angles.
18x +5 = (46) +(-1 +8x)
10x = 40 . . . . . . . . . . . . . subtract (5+8x) from both sides, simplify
x = 4 . . . . . . divide by 10
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Additional comment
The exterior angle is (18)(4) +5 = 77°. The marked unknown interior angle is -1+(8)(4) = 31°. The sum of the two remote interior angles is 46°+31° = 77°. The unmarked interior angle is 180°-77° = 103°.