Complete Grandad's proud text message to his grandson.

"It took a few weeks of practice, but I am finally used ___ with my thumbs!"

The correct answer is to typing.

The phrase "be used to" (meaning to be accustomed to something) is followed by a noun or a gerund (an -ing verb). Here, "to" is a preposition, not part of an infinitive verb, so it must be followed by "typing."