Replace the loading on the frame by a single resultant force. Specify where its line of action intersects member AB, measured from A.
Given:
{ F }_{ 1 } = 300 Ib\quad M = 600 Ib.ft
{ F }_{ 2 } = 200 Ib\quad a = 3 ft
{ F }_{ 3 } = 400 Ib\quad b = 4 ft
{ F }_{ 4 } = 200 Ib\quad c = 2 ft
\quad\quad\quad\quad\quad d = 7 ft