As you drive down a desert highway at night, an alien spacecraft passes overhead, causing malfunctions in your speedometer, wristwatch, and short-term memory. When you return to your senses, you can't tell where you are, where you are going, or even how fast you are traveling. The passenger sleeping next to you never woke up during this incident. Although your pulse is racing, hers is a steady 55 beats per minute. 

(a) If she has 45 beats between the miles markers posted along the road, determine your speed. 

(b) If you want to travel at 120 km/h, how many heartbeats should there be between mile markers?