Answer:  The ACSM (American College of Sports Medicine) guidelines recommend the following for most adults:

Cardio-respiratory Exercise (cardio):  Adults should get at least 150 minutes of moderate-intensity exercise per week.  This can be met through 30-60 minutes of moderate-intensity exercise FIVE days per week, or 20-60 minutes of vigorous-intensity exercise THREE days per week.  You can meet these requirements either in one continuous session OR multiple shorter sessions of at least 10 minutes to accumulate desired amount of daily exercise.

Resistance Exercise (strength training):  Adults should train each major muscle group 2 -3 days each week using a variety of exercises and equipment.  Two to four sets of each exercise will help improve strength.  For each exercise 8-12 repetitions can improve strength and power, 10-15 repetitions for middle-age and older persons and 15-20 repetitions to improve muscular endurance.  You should wait at least 48 hours between resistance training sessions.

Flexibility Exercise (stretching):  Adults should do flexibility exercises at least 2 - 3 days per week to improve range of motion.  Each stretch should be held for 10-30 seconds holding to the point of tension or "tightness".  Flexibility exercise is most effective and safe when the muscles are warmed up and will feel best after aerobic activity or strength training.

It is always important to check with your doctor before beginning an exercise program AND if you experience any unusual symptoms while exercising.