Denise and Tiffany are identical twins except that Denise weighs 220 lbs. and Tiffany weighs 110 lbs. They both walk on the treadmill with no incline at a speed of 3.5 mph for 30 minutes. Which of the following statements is correct? (30 seconds)

Denise's walking had a higher MET level than Tiffany's
Tiffany's walking had a higher MET level than Denise's
Denise burned more calories than Tiffany
Tiffany burned more calories than Denise
They both burned the same number of calories