Question 21643
well if bob is 52 then his mom was 77-52 when he was born or 25 years old.  Now if bob's sun is 38 then bob was 52-38 when his son was born or 14 old.  Now we could subtract 38 from 77 and get the moms age but since we know that she was 25 when bob was born we can just add 14 to that.  25+14 = 39 years old.