posted by ken .
A sign with a mass of 1000.0 kg is suspended from a wall with a cable that is attached to the wall at a point 3 m above a horizontal beam that causes the sign to be a distance of 4 m from the wall. What is the tension in the cable?
Well, you didn't say the mass of the beam. In practice, one cant ignore that.
Where the sign is attached, write vertical force equations (break tension into vertical and horizonal forces), horizontal forces.
Add them, in each case, they equal zero.
Finally, write the sum of moments about that point and set to zero.
It will solve.