The test was easy enough to finish within an hour.

[BLenn]

The test was easy enough to finish within an hour.

If this underlined sentence is incorrect when written "to finish", why is it awkward and incorrect when written "to finish"?
Is it correct to write the underlined part as "to be finished"?

 

[emsr2d2]

The test was easy enough to finish within an hour.

Source - test question.

If this the underlined part of the sentence is incorrect when written with "to finish", why is it awkward and incorrect? when written "to finish"?
Is it correct to write the underlined part as "to be finished"?

The original is correct and natural. Are you saying that the test says it's wrong? If so, the test is wrong! By the way, "test question" is not sufficient as a source. Please tell us the name of the book/website/test and name of author (if available).

We use "easy/difficult/hard to + base verb" all the time. Using "to be finished" there would be incorrect.