Answer :

naǫ
[tex]1 \ kg=1000 \ g \ - \ \$6 \\ 400 \ g \ - \ x \\ \\ \frac{1000}{6}=\frac{400}{x} \\ 1000x=400 \times 6 \\ 1000x=2400 \\ x=\frac{2400}{1000} \\ x=2.4[/tex]

400 grams of flour cost $2.4.