Clark will take 5 hours to catch Mitchell
Explanation:
It is given that Mitchell drives south toward Orlando at a speed of 60 miles per hour.
It is also given that Clark left 1 hour later travelling at a speed of 75 miles per hour.
The time taken for Clark is 
Thus, the distance for Clark is 
Clark catches Mitchell when their distances traveled are equal.
To determine the time it takes Clark to catch Mitchell is just to set the two distances equal.

Multiply 75 within the bracket,

Subtracting both sides by 75t, we have,

Dividing both sides by -15, we get,

Thus, Clark will take 5 hours to catch Mitchell.