To elaborate:
To do this problem, we assume that Mr. Sanchez is driving at a constant rate.
According to this information, he has driven 120 mi in 3 hr. To find how much he drives in 5 hr, we first have to find how many mi he drives in 1 hour. To do this, we divide 120 miles by 3 hours, since we assume that he managed to drive an equal amount in each hour.
120/3=40
Therefore Mr. Sanchez drove at a rate of 40 mph.
However, this isn't the final answer. 40 miles is the distance for one hour of driving. To find the distance for 5 hours, we have to multiply the distance by 5 as well.
40 times 5=200
In conclusion, Mr. Sanchez will drive 200 miles in 5 hours.