A 150- pound person burns 5.1 calories per minute when walking at a speed of 4-miles per hour. While walking, this person easts a snack that has 50 calories. This snack subtracts from the calories burned while walking. a. How long must the person walk at this speed to burn at least 180 calories? b. Describe when values the person could change so the amount of time spent walking would be less. Please help me if you can