[tex] 10^{3} [/tex] $1 bills is the same as [tex]10 \times 10 \times 10 = 1000[/tex] $1 bills.
You're told that 1000 $1 bills is 4.3 inches tall. That means to get the height of one $1 bill, you have to divide 4.3 inches (the height of 1000 $1 bills) by 1000 (how many bills there are): [tex] \frac{4.3}{1000} = 0.0043 in[/tex]
