Question 527458
Since there are 180º in a triangle, and we are given that it is a right triangle with angle 'a' being 40, that means that angle 'b' must be (90-40 = 50)º. We can then use the law of sines.

4/sin(40) = b/sin(50)

4sin(50) = bsin(40)

4sin(50)/sin(40) = b

b = 4.77

a^2 + b^2 = c^2

4^2 + (4.77)^2 = c^2

c = 6.22

Hope this helps!