Can you calculate what percentage of the remaining ballots Trump would need to win in Arizona?

Here is the answer. Imagine the 61,500 ballots are in two stacks, one for Trump and one for Biden. We will start by imagining that they are the same size, with both getting 50% of the vote. For the total number of votes to remain the same, any additional Trump votes must be matched by on equal decrease in Biden’s votes. For Trump to get 12,800 more votes than Biden, Trump would need an additional 6,400 votes beyond 50% and Biden would need to compensate by having 6,400 fewer votes than 50%. Trump’s share of the vote would then be 50% + 6400/61500 = 60.4%, which is very unlikely.

he needs 37,151 votes out of 61,500 to take the lead. That would be over 60% of the remaining ballots. Not impossible but highly unlikely, given that ballots left to be counted would lean towards Democratic ballots.