We're going to increase the intensity a bit but with slightly fewer hours than you did in Base3.
Great transition practice today! The Columbus triathlon club did these great R-B-R workouts called Hicks, or Hilly Bricks. The run was performed on a long hill with a flat bike. You can also do this with a bike trainer. Do a complete transition each time.
6 x (R 4:00, B: 15:00, R 4:00 ), rest 3:00 between
Be careful of run intensities…at only 4 minutes each it seems easy to do them fast, but 6 reps is a lot. Keep all efforts at RPE 3-4. Up the effort the last 2 if you've got anything left...