Steven is training for a race. He can currently run 1 mile in 7 minutes and wants to improve his time by 10 seconds each week until he can run one mile in 5 minutes. Which equation should Steven use to calculate the number of weeks (w) it will take him to reach his goal time of 5 minutes?
a) 7 - 10w = 5
b) 10w + 7 = 5
c) 10w - 7(60) = 5(60)
d) 7(60) - 10w = 5(60)