Reading the numbers
Eight-seven suited can be dealt 4 ways and a pair of aces 6 ways. Once both hands are out, the cards they share leave 24 possible pairings. Each row above stands for every pairing with the same suit pattern. The best case for 87s is 23.0%, the worst 21.9%: a shared suit takes away flush cards, and a suit held by both hands can split a flush.
Equity counts half of each tie, so it is the share of the pot 87s takes on average if the money goes in now. Compare it with the from the pot odds calculator. For a whole range on each side, use the range equity calculator.