FE Civil NCEES sample questions 60 & 61 structural

[lisfs]

I was hoping someone can help explaining questions 60 & 61 on the FE Civil NCEES sample exam.  I got the solutions, but they somehow skipped over the explanation part where they came up with the answers.  I've always struggled when it comes to determining whether a truss member is being subjected by Tension or Compression when a line of influence is given.  For some experienced structural engineers, they seem to be able to determine exactly whether it's Tension or Compression just by looking at the picture whereas I have to go through the lengthy analysis to figure it out.  Are there some tricks & tips of simply looking at the picture and know whether I should use Tension or Compression on an affected truss member?  Please share your experience. Thanks for your help.