Let the side length of the square ABCD be 6, and rotate 30 degrees clockwise around point a to get the square aefg, where the side FG and BC intersect at h, and find the length of BH
The intersection I of the extension line of AB and GF
AI=AG/cos30°
BI=AI-AB
BH=BI/tg30°
AG=AB=6
The rest is up to you