Question 768276
Generalizing in order to solve symbolically,
Let d = 3000 miles between locations
 let x = time in hours until subjects meet
p = speed of Sol, 200 mph
r = speed of Robert, 400 mph
notice p<r.


During unknown time x, Sol and Robert move their distances, and the sum of their distances is d.

{{{highlight(r*x+p*x=d)}}}
{{{(r+p)x=d}}}
{{{x=d/(r+p)}}}_____The Answer in Symbolic Form.


Just substitute the given numeric values to find x.