What is (x+3i)(x-3i)(x+1)(x-1) multiplied out?

We can start with the first two sets

(x+3i)(x-3i) = x²-9i² then simplify it to x²+9

multiply the next two

(x+1)(x-1) = x²-1

then multiply those two together

(x²+9)(x²-1) = x∧4-x²+9x²-9

combine like terms x∧4+8²-9

that is your answer