Explanation:
Switching from walking to taking the bus would mean a behavioral change that will result in a decrease in activity level. Whereas you were getting some form of physical activity in walking you are now taking the bus which means your level of physical activity has dropped as you will be sitting on the bus not doing anything, before you were actively moving your body.
A woman needs 2000 calories a day while a man needs 2500 calories a day. Study your current weight and see whether it meets the requirements for your gender to better calculate your needs.