While riding her bike to the ocean and back home 7 times, Christine timed herself at 45 min, 58 min, 49 min, 44 min, 52 min, 48 min, and 52 min. She had set a goal of averaging 51 minutes for her rides. How many minutes will she need to spend on her eighth ride to attain her goal?
a) 45 min
b) 51 min
c) 55 min
d) 56 min