The approximate value of 5.5 million x 1.9 thousand is
(scientific notation)

The answer is:  " 1.045 * 10¹⁰  " .

Explanation:

 "5.5 million = 5,500,000 = 5.5 * 10 ⁶ "  ;

 "1.9 thousand = 1,900 = 1.9 * 10³  "   ;

   So;  "5.5 million * 1.9 thousand" ; 

  =  (5.5 * 10 ⁶) * (1.9 * 10³) =  5.5 * 10⁶ * 1.9 * 10³ ;
 
     =  5.5 * 1.9 * 10⁶ * 10³ ;
 
    Note the following properties of exponents:

    xᵃ * xᵇ  =  x⁽ᵃ⁺ᵇ⁾ ;


As such, " 10⁶ * 10³  = 10⁽ ⁶ ⁺ ³⁾  = 10⁹ " ; 

So; rewrite:  

5.5 * 1.9 * 10⁶ * 10³  ;

= 5.5 * 1.9 * 10⁹   ;

    5.5 * 1.9 = 10.45 ;

Rewrite as:  " 10.45 * 10⁹ " ;

In scientific notation, we need to rewrite as an single digit integer, followed by a decimal and other values (if applicable); following by * 10 raised to the appropriately adjusted exponential power.

As such, we write the value as:

   " 1.045 * 10¹⁰  " .