it 2 cars leave at the same time on 30 mph and the other 46

it 2 cars leave at the same time on 30 mph and the other 46 mph at what point will they be 72 miles apart? I have in diagram:
distance mph time
d 30 t
d+72 46 t
is this correct? what would be my finale answer?

Solution

You know this is RTD. Here is a chart to help
cars . . . . . . . .rate . . . . . . . . .time . . . . . . . . distance
1 . . . . . . . . . . 30 . . . . . . .. . .t . . . . . . .. . . . . 30t
2 . . . . . .. . . . .46 . . . . . .. . . . t . . . . . . .. . . . . 46t
totals . . . . .. . . . . .. . . .. . . . .. . . . . .. . . . . . .. .72
46t - 30t = 72
16t = 72
t = 72/16
t = 4.5 hours