(2.5 x 10 to the -8 power)x(9 x 10 to the -10 power)

A2.25 x 10 to the -18 power

B.2.25 x 10 to the -19 power

C.2.25 x 10 to the -16 power

D.2.25 x 10 to the -17 power

sorry i couldn't write exponents