Please solve this question in details and explaination. Thanks so much in advance. For momentum equation, please explain it clearly to me, this part makes me so confusing.

ME. 1.8 Chap 07 (Frame 2) Find the internal normal, shear and moment in the column at point D when the load is in the position as shown. Points B, E, and F are pins. BH is a short support link. 3 ft 5 ft 3 ft O 1 ft OB . C H G D 2 ft the 3 ft 750 1b A