How do you know w/o calculator? plz

In the diagram of circle a what is m

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Meghan has created a diagram of her city with her house, school, store, and gym identified. a. how far is it from the gym to the store? b. meghan also wants to walk to get some exercise, rather than going to the gym. she decides to walk along arc ab. how far will she walk? round to 3 decimal places.