(2.1*10^-7)(3*10^-6) write answer in scientific notation

(2.1 x 10^-7) x (3 x 10^-6)  =  (2.1 x 3) x (10^-7 x 10^-6)  

     =  6.3 x 10^-13                    (when multiplying numbers with the same base, add their exponents)