If P × Q means P is the father of Q, P - Q means P is the son of Q, and P + Q means P is the daughter of Q, what is the relationship of R if P × R + Q = true?
Four friends - Alex, Brian, Charlie, and David - have different favorite colors: Red, Blue, Green, and Yellow. Alex does not like Blue or Green. Brian's favorite color is not Red. Charlie likes Green. What is David's favorite color?