Part A:
An isometric transformation is a type of transformation where the original shape and size of the pre-image is not altered in the image.
To show that the translation was an isometric transformation, we show that the distance between any two points in the pre-image is equal to the distance between the corresponding points in the image.
Consuder, line AB, the distance between point A and point B is given by:

The distance between point A' and point B' in the image is given by:

Similarly checking other points of the pre-image against the corresponding points of the image shows that the size of the pre-image is preserved in the image.
Part 2:
The translation that maps the triangle ABC onto its image are:
Triangle ABC was shifted 4 units to the right.
Triangle ABC was shifted 4 units up.
Speed of Tim = 60 miles/hour
Speed of Joe = 45 miles/ hour
Distance = Speed x Time
A 3 hours, Tim had travelled 60 x 3 miles = 180 miles.
At 3 hours, Joe had travelled 45 x 3 miles = 135.
The difference between the distances is 45.
Therefore, they were 45 miles apart after 3 hours.
I hope this is right.