Divide that number by three and use it as your target number for each set. Do the same for the sit-ups. Do four sets of regular push-ups in 40 second sets with one minute rest between each set.
Form is important.
If you can not do the push-ups properly, go to your knees and continue until you have finished the sets. After three workouts, add three push-ups to each set. Do four sets of regular sit-ups in 40 second sets with one minute rest between each set. If you can not do all the sit-ups properly, lower the angle of your legs until they are almost parallel to the ground. After three workouts, add three sit-ups to each set.