This bike workout will be a trainer workout at the gym. For the first 10 minutes, put your bike in an easy gear maintaining a 90-95 cadence. This will loosen your legs up from the swim and warm them up. The last 20 minutes you can increase the resistance to a normal workout.
Swim 400 continuous. The first 300 will be at a pace you can sustain without problem while the last 100 will be at a faster pace. Try to make your last 25 as fast as you can while still maintaining good form.
This workout will be followed by a bike trainer workout at your gym. Try to make the transition as quick as possible.