By the , the sum of the angles in a triangle is equal to 180°. therefore, m∠a+m∠b+m∠c=180° . using the , (6x)°+90°+(x+6)°=180° . to solve for x, first combine like terms to get 7x + 96 = 180. using the , 7x = 84. then, using the division property of equality, x = 12. to find the measure of angle a, use the substitution property to get m∠a=6(12)° . finally, simplifying the expression gets m∠a=72° .