A football quarterback is moving straight backward at a speed of 2.00 m/s when he throws a pass to a player 18.0 m straight downfield. The ball is thrown at an angle of 25.0 relative to the ground and is caught at the same height as it is released. What is the initial velocity of the ball relative to the quarterback ?

So i've referred to this https://www.youtube.com/watch?v=xB4cGnEneNc&list=PL_3h4GvKc6GCfxVJxw61h_Ei5LxigOonr&index=56 as a solution but he uses a formula that won't be on my given formula sheet, so I don't want to learn this method if I can avoid it... I'm wondering if you have another way.