(2x10^3) x (2x10^6) x (2x10^12) = ?

Multiply the 2's together:
2 x 2 x 2 = 8

Multiply the 10 with exponent terms together:
10^3 x 10^6 * 10^12 = 10^(3 + 6 + 12) = 10^21

Group both results:
8 x 10^21