a+b = 110
a-b = 30
Adding the 2 equations together you get,
2a = 140 => a = 70
substituting into one of the above equations, you get b = 40 ( 70-40 = 30)
Knowing that the sum of the interior angles of a triangle is equal to 180, you can find the remaining angle by c= 180 - (a+b)
so, c =70.
Therefore the smallest angle is angle b = 40.