Worth vs. worthy

[Fairy]

Test No. errors/elem-8 "A Change of Heart", question 6

Don't be stupid - it's just not worthy it, you know why.

(a) stupid
(b) worthy
(c) know

Test No. errors/elem-8 "A Change of Heart", answer 6

Don't be stupid - it's just not worth it, you know why.

Correct entry: worth
The error was: (b) worthy

You have found the error but your entry is incorrect.
Don't be stupid - it's just not worthy it, you know why.
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"worth" and "worthy" are an adjective, so why this sentence use "worthy" in stead of "worth". I don't understand? They have the different meaning?

[Mister Micawber]

.
Usage requires

To be worth + complement -- It is not worth the trouble.

To be worthy of + prep obj -- She is not worthy of my love.
.
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Native English teacher at Mister Micawber's

[Fairy]

Thanks a lot