Respuesta :

Answer:

Step-by-step explanation:

Sum of angles inside triangle is 180

b + (a -3) + 90 =180

b + a - 3 + 90 = 180

b + a +  87 = 180

b + a +  87 -87 = 180-87

b + a  = 180-87

b + a  = 93

b = 93 -a