James=28 km/h; (4+x) hours
Julio=35 km/h; 4 hours
Our first priority is to check for consistency of units. For example, is any information provided in minutes or miles. Everything is consistent, in kilometers and hours, so we may proceed.
We know that both men traveled the same distance when Julio caught up with James.
(28 km/hour)[(4+x)hours]=(35 km/hour)(4 hours)
Let's cancel units where appropriate...
(28 km/hour)[(4+x)hours]=(35 km/hour)(4
Let's proceed to cancel units where appropriate...
(28 km)(4+x)=(35 km)(4)
Cancelling units is always your first priority, before calculations. This is because if the units are not aligned, you are working with the wrong equation.
Let's subtract 112 from both sides as we proceed to isolate x...
James traveled 1 hour + 4 hours=5 hours