$3,5\cdot {10}^{-12}\cdot 2=7\cdot {10}^{-12}$

$2,5\cdot {10}^{-4}\cdot 3\cdot {10}^{-6}=7,5\cdot {10}^{-10}$ $2,5\cdot {10}^{-4}\cdot 3\cdot {10}^{-6}=7,5\cdot {10}^{-10}$

$7\cdot {10}^{-9}\cdot 1,2\cdot {10}^{-12}=8,4\cdot {10}^{-21}$

$7\cdot {10}^{-13}\cdot 5\cdot {10}^{-3}=35\cdot {10}^{-16}=3,5\cdot {10}^{-15}$

  $6\cdot {10}^{-3}\cdot 9\cdot {10}^{-6}=54\cdot {10}^{-9}=5,4\cdot {10}^{-8}$  

$5700\cdot {10}^{-12}\cdot 0,1=570\cdot {10}^{-12}=5,7\cdot {10}^{-10}$