Please, need help selecting the right motor for a design I am building.

Can someone please help answer my question and also show me how to solve this problem for myself? I am wanting one 40lb metal triangle to rotate up 90° in 6 seconds. Its base will connected by hinge to the base of another triangle. The base is 67.88", the other legs being 48", and a height of 57.87".By rotating the apex of the triangle 90° the apex would travel an arc by 8.18ft. I intend to use two spockets and a chain connected to a gear motor. What size of motor will I need to use to complete this and how was it determined? Please help, Thanks