How to subtract decimals???

Task description: We got the task to subtract decimals. And also we learnt how to takeaway decimals but first we had to learn place value of decimals. For e.g 0.897.. what is in the tenths spot "8". This like that. 

I would rate this task for difficulty would be a 2/10. I thought that this task was to easy in a way. in the future I would like a harder task.