4 X/wk, 40min each
How much exercise
and what type(s) one should do is quite variable, dependent on age, physical condition, weight, medical illnesses, muskuloskeletal problems, conditioning status.
In general, start low and build up to goal, both in time and intensity. Would recommend aerobic (treadmill, outdoor walk, elliptical, swim) above amt. Some resistance training also. If some part of body hurts, stop stat.