vectors/displacement problem

Quote:

A jogger travels a route that has two parts. The first is a displacement **A** of 2.90 km due south, and the second involves a displacement **B** that points due east.

Quote:

(1) The resultant displacement A + B has a magnitude of 4.55 km. What is the magnitude of **B**?

What is the direction of **A + B** relative to due south?

(2) Suppose that **A - B** had a magnitude of 4.55 km. What then would be the magnitude of **B** and what is the direction of **A - B** relative to due south?

direction of **A - B** relative to due south

for part1:

$\displaystyle A^2+B^2+C^2 = 0 $

**B** = $\displaystyle \sqrt{A^2+(-C^2)}$

**B** = $\displaystyle \sqrt{(2.9)^2+(-4.55)^2}$

**B** = 5.395 km

some how that answer is wrong, can someone explain?