I am on bart, so it's 'character sketch by description' time.
a. Woman; long blondy-brown hair, quite straight; she has frown lines on her forehead and a tight angry face; she is looking out the window when she isn't looking shiftily around the car.
b. Boy; straight blond hair; blue, heavy coat with hood; he has rollerskates with him; he looking out the window; alert, reasonably intelligent looking.
c. 'a' left. 'c' took her seat in the corner. She (woman) is staring at the back of 'b''s head. This can get boring, no wonder Harriet the Spy didn't write volumes.