I am in a fitness class and our assignment is to create an exercise program. It has to have a warmup, exercise, cool down, and stretching. I am set with everything except the exercise. I found some online using dumbbells, and I know I will be using 5lbs ones. What I need to know is how many reps I should do or whatever that part is.

Here’s what I have for my exercise plan:
Step one: Dumbbell press (chest and shoulders)
Sitting on bench or chair, hold 2 5lb dumb bells together at shoulder level with palms facing in. Rotate your palms forward as you lift your elbows up and in line with your shoulders. Return to starting position and repeat

Step two: Dumbbell curls (biceps)
Keep elbows tucked into waist, palms are facing out. Curl weights up towards body, i.e. biceps curl. Return to starting position and repeat.

Step three: Kickbacks (triceps)
Put one knee on bench, other foot on the floor. Take weight into one hand. Support your body with other hand on the bench. Bend at waist until your upper torso is horizontal. Lift your upper arm to your side and pull it close to your body. Bend your elbow into a right angle. Straighten your arm behind your torso. Only forearm moves. Return to starting position and repeat. Reverse arms.

Step four: Dumbbell row (back)
Support yourself again on a bench. This time, start with weight in hand down to the floor. Pull elbow up and in to torso. Contract your shoulder blades. Return to starting position and repeat. Change to other arm.

Those four steps need to fill up about 45min of exercise times so how many reps should I do for each one and how should I write it in my program? How long does it take for each rep? What is a rep?! Help!