A train leaves a station traveling at 600 km/hr. 3/4 hr later another
train leaves the same station traveling 800 km/hr. How long will it
take the second train to overcome the first?

Dear kike442,

In 3/4 = 0.75 hours, the first train has traveled

  0.75 * 600 = 450

kilometers.

If the second train catches up to it x hours later, the first train
will have traveled

  600x + 450

kilometers in total. The second train, for its part, will have traveled

  800x

kilometers.

But these distances are equal, so we have the following equation.

  800x = 600x + 450
  200x = 450
     x = 450/200
       = 9/4
       = 2.25

Thus, the second train will take 2.25 hours, or 2 hours and 15
minutes, to overtake the first.

Regards,

leapinglizard

thanks a million, saved me a bunch helping with homework