In this case, Katherine was experiencing pain in the neck because she has been many hours working and she is stressed.

You should relax a bit.

You should rest and take some breaks from time to time.

You should meditate, go for a walk, sleep more, do some exercice, etc

You must organize your time better.

You must go to the doctor if your neck hurts.

You must take breaks every 30 minutes that you are studying.

She is adict to the technology.

You shouldn't use the technology.

You must use the technology.

You musn't use the mobile phone at night.

You should study more but not with the mobile phone.

Aroa is obsessed with TV and watches youtube.

Play sports, you can also read , do homework or go for a walk with friends.

You musn´t limited time with TV.

You musn´t take away the TV remote.

You must do homework.

You must help at home.

Alex is sad, he feels anxious and bad because he plays computer games a lot.

You should start a new hobby

You mustn't play computer games so much.

You should start meeting your friends again.

You mustn't use technology so much.

You mustn't play computer games so much.