Question 917069

Dora drove east at a constant rate of 75 kph. One hour later, Tim started driving on the same road at a constant rate of 90 kph. For how long was Tim driving, before he caught up to Dora?

I have tried to use a table
i set it up like this
Name|D(mi)|R(kph)|T(hr.)|
Dora|  d  |75    |t     |
Tim |  d  |90    |t+1   |
and then I went and i tried to put it into an equation
75t=90(t+2)
75t=90t+180
-90t -90t
-15t=180
____ ____
-15  -15
t=-12
but It is not an answer on my multiple choice and it wouldn't be a negative 12 hours
-15 
<pre>
You should let time that it takes Tim to catch up to Dora be T
Since Dora will take a longer time as she's travelling at a slower rate of speed than Tim, time she'll take is: T + 1
Thus, your equation is: 90T = 75(T + 1)
Solve for T, the time Tim will take.