Yes they do. In order to do this you must make the fraction 70/2 and 105/3. If you divided each one of those you get 35 for both which means it's a proportion.
I believe that the answer for y is...
y= -ax+c/b
For this case we have to write the equation of the position of each one.
We have then:
For the robber:

For the marshall
:


By the time the marshall reaches the robber we have:

From here, we clear the time.
We have then:




Answer:
it takes the marshall to catch up to the robber about 2.7 hours.