Answer:
After 11.25 hour Mrs. Caldwell catches Mr. caldwell
Explanation:
We have given that Mr. caldwell leaves 2.5 hour before Mrs. Caldwell.
Let the distance is d
When Mrs. Caldwell catches Mr. caldwell they will cover same distance as d
Speed of Mr. caldwell is 45 mph
And speed of Mrs. Caldwell. is 55 mph
Let time taken by Mrs. Caldwell is t
Then time taken by Mr. caldwell is t+2.5
So



So after 11.25 hour Mrs. Caldwell catches Mr. caldwell