In the country of Ouguo, everyone hates odd numbers so much that they don't even want to see any odd number digits. Therefore, they use marks to replace odd number digits when communicating. For example: when people in Ouguo write “$3 \times 4=12$”, they write it as “ふ $\times 4=ふ 2$”.
Convert the subtraction equation in Ouguo “出 66 - ※ 出=还原 to a normal equation, there are
$\qquad$ possible ways.
$6$