Simplify the following:

(3x - 4y - 2)(3x - 4y - 6)

Let (3x - 4y) = z

Then the given expression = (z - 2)(z - 6)

We know that (x - a)(x - b) = x² - (a + b)x + ab

∴ (z - 2)(z - 6) = z² - (2 + 6)z + (2)(6)

= z² - 8z + 12

= (3x - 4y)² - 8(3x - 4y) + 12

= (3x)² - 2(3x)(4y) + (4y)² - 24x + 32y + 12

= 9x² - 24xy + 16y² - 24x + 32y + 12