Answer:
x=13
Explanation:
The sum of the angles of a triangle add to 180 degrees
3x+ 4x-1 +90 =180
Combine like terms
7x +89 = 180
Subtract 89 from each side
7x +89-89=180-89
7x =91
Divide each side by 7
7x/7 =91/7
x = 13
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