Translation:I'm not busy.
Hi, it explained in the Tips section that when you're using 不 (not) you don't need 很 to connect the subject to the adjective. Remember, 很 does not translate to the english verb 'to be' but is used in place of a verb here.
你们都很忙。 You all are busy. 你们都不忙。 You all aren't busy.
我不忙。 I'm not busy. 我很忙。 I'm busy.
In a sentence with a verb you just add the 不 in front of the verb: 不是 不叫
Here 忙 is not an adjective (like adjectives in English). Technically, you must use the suffix -的 to mark an attribute of an object. The following sentence is grammatically correct:
我不是忙的。(this is an very awkward expression, don't say this in real life)
The usage of 忙 itself is somehow similar to a verb. Thus 我不忙 is a correct expression. If you know Japanese and Korean, you'll see similar phenomena in these languages too.