Expanding each term:

$(a-1)^2 = a^2 - 2a + 1$$(a-2)(6-a) = 6a - 2a^2 - 12 + 2a = -2a^2 + 6a - 12$$135(a-4)^2 = 135a^2 - 1080a + 2160$$(a-4)(7-a) = 7a - a^2 - 28 + 4a = 11a - a^2 - 28$$18a = 18a$$6 = 6$

Now, putting all these terms back together and simplifying:

$(a^2 - 2a + 1) + (-2a^2 + 6a - 12) - (135a^2 - 1080a + 2160) - (11a - a^2 - 28) - 18a + 6$

which simplifies to:

$-137a^2 + 1097a - 2173$