ForA, use Pythagoras:
the triangle with AB is just the other triangle flipped, and its base is half of the entire line given, as the line given is the width of the two put together. so it's 6.2/2 = 3.1
a^2 + b^2 = c^2
1.4^2 + 3.1^2 = c^2
take the square root of the answer, which is c, and it...