For the given expressions:

(3x²-3)(9x⁴+9x²+9)
= 3x² 9x⁴ + 3x² 9x² + 3x² 9 - 3 9x⁴ - 3 9x² - 3 9
= 27x⁶ + 27x⁴ + 27x² - 27x⁴ - 27x² - 27
= 27x⁶

(5x²+6)(25x⁴-30x²+36)
= 5x² 25x⁴ + 5x² -30x² + 5x² 36 + 6 25x⁴ - 6 30x² + 6 36
= 125x⁶ - 150x⁴ + 180x² + 150x⁴ - 180x² + 216
= 125x⁶ + 216

(8b²+4)(64b⁴-32b²+16)
= 8b² 64b⁴ + 8b² -32b² + 8b² 16 + 4 64b⁴ - 4 32b² + 4 16
= 512b⁶ - 256b⁴ + 128b² + 256b⁴ - 128b² + 64
= 512b⁶ + 64

(7a²-4)(49a⁴+28a²+16)
= 7a² 49a⁴ + 7a² 28a² + 7a² 16 - 4 49a⁴ - 4 28a² - 4 16
= 343a⁶ + 196a⁴ + 112a² - 196a⁴ - 112a² - 64
= 343a⁶ - 64

Therefore, the expanded forms for the given expressions are: