Answer:
x = 13
Step-by-step explanation:
The sum of the 3 angles in a triangle = 180°
Sum the given angles and equate to 180, noting that ∠ C = 90°
3x + 4x - 1 + 90 = 180, that is
7x + 89 = 180 ( subtract 89 from both sides )
7x = 91 ( divide both sides by 7 )
x = 13
