draw an arrow going 30m to south and label the distance (30m). Then, at the end of it, draw an arrow going 30m to east, then label again. Now, draw an arrow from the original position to the end of the last arrow and label its distance using Pythagorean theorem.
Looking at my picture may help more.
This is probably what you want.
I will assume you know how to solve Pythagorean Theorem.
Edit: I forgot to specify 30m for East, now it's fixed
