When it comes to building muscle and burning fat the most important form
 of exercise that you can do is strength training. This should take 
priority over cardiovascular exercise.
However, cardio still 
plays an important role in your overall workout routine. Cardio can help
 to improve your endurance, increase your overall activity level, and 
burn more calories. 
But this isn't a 
"One Size Fits All" answer for how 
much cardio you should do. It really depends on your lifestyle, your 
body type, and your fitness goals.
Just check out my most recent "
Ask Lee Video Q & A" to find out how much cardio you need to do...