$$ (6a-7)^2 - (4a-2)^2 = ((6a-7) - (4a-2))((6a-7) + (4a-2)) = (6a - 7 - 4a + 2)(6a - 7 + 4a - 2) = (2a - 5)(10a - 9) $$.
Ответ: $$ (2a - 5)(10a - 9) $$.