#### Answer

$9,994,433$

#### Work Step by Step

Given the numbers $4, 3, 9$ we will use each digit at least two times to write the largest seven-digit number possible.
The largest digit is $9$. We will place the largest digit ($9$) in the three largest valued columns (one-million, 100-thousands, and ten-thousands).
Next, we will place the second largest digit ($4$) in the next two largest valued columns (thousands and hundreds).
Next, we will place the third largest digit ($3$) in the next two largest valued columns (tens and ones).
$9994433$
Separate each group of three digits with a comma.
$9,994,433$