This sentence is from a TOEFL material:
According to the news report, this investment by the company will likely provide a major boost to the economy because it will lead to the development of new technologies for export.
I usually put preposition to after the adverb likely, but here in this sentence, the word clearly hasn't been used that way.
Now I'm confused about when to put preposition to after the adverb likely.
Will this sentence still be grammatical if I put preposition to after the adverb likely? If so, why then is the preposition to omitted in this sentence?