Lisa leaves her house for a road trip and drives at a rate of 50 mph. Keisha leaves her house 1 hour later and drives along the same route at a rate of 60 mph. At any given time t, the distance traveled can be calculated using the formula d = rt, where d represents distance and r represents rate. Which system of equations can be used to find how long after Lisa departs her house she is passed by Keisha?
A) d=50t
d=60t-1
B) d=50t
d=60(t-1)
C) d=50t
d=59t
D) d=50(t-1)
d=60t