TUTOR HW need explanation pls

I can try to explain but if you dont want to use it That is fine, 

It is an Isosceles acute triangle, Angle A Is at the bottom Left, C as at the top, and B is at the bottom right.  Angle C is 45 degrees, and the length of cb and ac is 3, They are the two side lengths. That is all the info I have to find the area and I am stuck, I need an actual explination If that is fine, I didnt understand how my tutor explained to me and ill ask him again next  monday, But for now I need explination.

I just realized this hw my tutor gave me is the same thing, my  geometry class had what?! good thing no one answered and i figured it out

That is excellent Krxzy