The three inside angles of a triangle equal 180 degrees.
All the 3 given angles together to equal 180 to solve for x, then calculate angle A.
x + (x-8) +(3x+13) = 180
Simplify the left side by combing like terms:
5x +5 = 180
Subtract 5 from each side:
5x = 175
Divide both sides by 5:
x = 175/5
x = 35
Now x is known, replace x in the equation for angle A:
3x+13 =
3(35) +13 =
105+13 = 118
Angle A = 118 degrees.