Suppose that the triangle ABC has A = 90⁰, B = 60⁰, AB = 4.  We construct the rectangle ABCD with center O.  By the assumption B = 60⁰ , assune that OAB is a equilateral triangle; OB = AB = 4, BC = 8. By the theorem Pytagor we have

\(AC=\sqrt{BC^2-AB^2}=\sqrt{8^2-4^2}=4\sqrt{3}\).  So  \(BC=8,CA=4\sqrt{3}\).

It so good for me in the future , thanks you :))