removing the dimensional prefix and express in scientific notation ( include unit)

7.4nm
6.78 x 10^8 MHz
5.36 x 10^6 kV
1500mA

Calculate the following numbers into scientific notation (include units)

7800nm + 95pm =
2500nm - 7pm =
(65x10^4m) x (4.5x10^-6s-1)=
(24x10^5m) / (2x10^-8s) =

convert the following to the prefix commonly used (use units)
55 000 000 Hz
4.8x10^4V
0.0068s
0.00000000234m