Answer:
Step-by-step explanation:
By the triangle sum theorem, the sum of angles in a triangle is equal to 180°. Therefore m∠A + m∠B + m∠C = 180 using the Substitution property (3x)° + 90° + (x+10)° = 180° To solve for x, first combine like terms to get 4x + 100 = 180, using the subtraction property of equality, 4x = 80 using the Division property of equality, x = 20. To find the measure of the angle A, use the substitution property to get m∠A = 3(20)°. Finally simplify the expression gets m∠A = 60°
