m∡A = 70º
1) Considering that the Sum of the interior angles within a triangle is always 180º
2) We can write the following, and solve for x
x+80 + x +80 +40 = 180
2x +160 +40 = 180
2x + 200 = 180
2x =180-200
2x= -20
x=-10
3) So since angle A = x +80, we can plug it into that the value of x
m∡A = x +80º
m∡A=-10+80
m∡A = 70º