Let’s resolve into factors

(p²-3q²)² - 16(p²-3q²) + 63

To resolve it into factors we first resolve 63

63=7×3×3

Given, x² + (m + n)x + mn=(x + m)(x + n) … (2)

Comparing 1 and 2

m + n = -16

mn =63

∴ (1) can be written as

(p²-3q²)² - 9(p²-3q²) - 7(p²-3q²) + 63

=[{(p²-3q²) - 9}{(p²-3q²) - 7}]

∴ the resolved factors are [{(p²-3q²) - 9}{(p²-3q²) - 7}]