Well, 'Intro to Structural Engineering' is different than 'Intro to Engineering', but usually cable problems are reserved for later studies. Nevertheless, the same concept applies when determining forces: You can easily determine the vertical component of the support reactions by looking at the entire system and summing forces in the y direction: due to symmetry, half of the vertical load from the distributed load will be supported at the left support, and the other half at the right support. But that won't give you wire tensions, or horizontal components of the reaction forces at those supports. To do so, isolate the cable in a free body diagram that encircles the left support and the left half of the cable, cutting thru the cable at midpoint. At the midpoint, only the tension force, T_h, acts horizontally; there is no vertical component at that point, because cables cannot support shear (cables tensions always act along their longitudinal axis, parallel to the tangent of the cable curve at that point). Now just sum moments about the left end to solve for T_h. That should get you started, at least.
