THIS IS URGENT I NEED HELP ASAP.(9x 10^-3)^2

simplify. write in scientific notation
a 8.1x10^-5
b 81x10^-4
c 81x10^-3
d 8.1x10^-6
Evaluate 1/2a^-4b^2 for a =-2 and b=4
a2
b 1/2
c3
d4
is the following statement always, never, or sometimes true?
a number raised to a negative exponent is negative?
A always
B never
C sometimes