@uTep2Step
For how many calories you burn a day at rest/without activity :
3.5 X (your weight in kilograms) /1000 X 5 X 60 X 24
For how many calories a certain activity burns, it's more difficult to assess if it's something other than running. But in general you can google the MET equivalent of activities and you'll see a huge list (running, weight lifting etc).
So take the METS of an activity X 3.5 X(your weight in kilograms)/1000 X 5 X however many minutes you do that activity X however many days a week you do that activity. That will give you the calories an activity burns in a week.
For the amount of weight you want to lose:
1 lb= 3500 calories. However many lbs you wanna lose, multiply that by 3500 and that's the amount of calories you need to either burn, or eat less than you currently eat.
If you have that number of calories that you need to burn to lose your goal amount of weight, just divide that number by the amount of calories you burn in a week from whatever activity you calculated above and that will tell you how many weeks it will take you to lose the weight from that activity.
Did any of that make sense haha?