Physics question resultant velocity

Hi, please can i have help on this question? I don’t understand how to draw the resultant velocity line? I basically drew a line horizontal to the boat velocity and then a line spilitting the two lines. I thought this old be the resultant velocity but I don’t think that’s right?
Here is the question: https://app.gemoo.com/share/image-annotation/586220827149328384?codeId=P5Gaw3qGV3AlX&origin=imageurlgenerator
Thanks