https://www.youtube.com/watch?v=Ttdzw_350ZI - column addition
https://www.youtube.com/watch?v=IzlyN2-uLSU- column subtraction
https://www.youtube.com/watch?list=PL_veIGcSU3qzKJNmGWsnvTzs6Kd9kwCpd&time_continue=231&v=3kxpZQ4Ivtg&feature=emb_logo- place value
https://www.youtube.com/watch?v=eO8rJRBZzAQ- multiplication
https://www.youtube.com/watch?v=gAd85C4uWqw&feature=emb_logo- division