An inequality can be formed by simply translating the problem statement to numerical expressions.
From the problem we know that

added with

hours should be equal or greater than

(helpful insight from the keyword "at least"). Therefore, it's inequality would look like:

(>= is used instead of ≥ for constraints in formatting)
The inequality above best models the situation.
Yes, EF is parallel to CD. Translation is the simple slide of a shape, therefore it doesn't have an effect on parallel lines.
It should always have the same perimeter if it stays the same geometric figure.
60$. These are my equations :
600 * 0.2 = 120 ; 600 - 120 = 480
Then...
600 * 0.1 = 60 ; 600 - 60 = 540
Which then became....
540 - 480 = 60