5.3.2.22 Various Problems in the Space

Condition: B rectangle \ (A B C D \ Quad A B: A D = 2: 3 \). Through the side \ (b c \) a plane \ (b c e \) was drawn, from which the diagonal of the rectangle forms an angle equal \ (\ alpha \). Find the angle between the planes \ (b c e \) and \ (a b c \) in cases where \ (\ alpha \) takes the value \ (30^{\ circ} \).