“Easy”, “Difficult” + to-infinitive
Incorrect : English is not easy to be learnt.
Correct : English is not easy to learn.
Incorrect : This sum is difficult to be done.
Correct : This sum is difficult to do.
Incorrect : The problem is hard to be solved.
Correct : The problem is hard to solve.
Note: The adjectives “easy”, 'difficult', 'hard', 'heavy', “good” etc are usually followed by the active infinitive (to + base form of a verb), not by the passive infinitive (to + be + past participle form of a verb).