5. Do not use could to talk about something that you succeeded in doing.I managed to run 10 km yesterday in under an hour. (NOT I̶ ̶c̶o̶u̶l̶d̶ ̶r̶u̶n̶ 10 km yesterday...)
How many eggs were you able to get? (NOT ...I̶ ̶c̶o̶u̶l̶d̶ ̶get.)
For more details, see Practical English Usage 3rd Edition 122.