i. 16xy × 18xy
= 16 × 18 × xy × xy
= 288x²y²
ii. 23xy² × 4yz²
= 23 × 4 × xy² × yz²
= 92xy³z²
iii. (12a + 17b) × 4c
= 12a × 4c + 17b × 4c
= 48ac + 68bc
iv. (4x + 5y) × (9x + 7y)
= 4x × (9x + 7y) + 5y × (9x + 7y)
= (4x × 9x) + (4x × 7y) + (5y × 9x) + (5y × 7y)
= 36x² + 28xy + 45xy + 35y²
= 36x² + 73xy + 35y²
