Question

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

Answer 1

Answer: 5 hours

Explanation:

TABLE

People D(mi.) R(mph) T(hr.)

Dora 75(t+1) 75mph t+1

Tim 90t 90mph t

90t = 75(t+1)

90t = 75t +75 -Use Distributive Property

15t=75 -Subtract 75 both sides

t=5 - Divide 15 both sides

Tim was driving for 5 hours before he caught up to Dora.

Answer 2

Ok so let T=time from when Tim starts
Distance Tim travels= T*90
Distance Dora travels=T*75 + 75 (<as already started)
for him to have caught up His distance must equal hers so:
90T=75T + 75 (now minus 75T)
15T=75 (now divide by 15)
T=5 :)
So five hourse, hope this helped :)