you draw a line upward 13km and draw another one to the right 24km then draw another one down 6km, now you join the the last line to the original starting point.
Step 2: after drawing the diagram above you should draw a doted line from the end of the last line due south to bisect the first line due north and label the line 24km also since it forms a rectangle.
step 3: it now forms a right-angled triangle at the bottom then you apply the Pythagoras theorem