#### Answer

$-4.05 \times 10^{-9}$

#### Work Step by Step

To write the number in scientific notation, do the following steps:
(1) Move the decimal point 9 places to the right to have $-4.05$
(2) Multiply by $10^{-9}$ to retain the original value and find: $-4.05 \times 10^{-9}$