These are the answers:
1. They are similar because their corresponding angles are congruent.
2. They are not similar because their corresponding side lengths are not proportional.
Similar rectangles, in their simplest definition, are rectangles that have the same shape but dissimilar sizes. You can't say they are congruent rectangles because "congruent" means equal in shape, sizes or lengths.
They are not proportional because they don't have the same ratio/fraction.
4:3 is not equal to 6:4
Hope this helps :)