You have the following Mixed number:
[tex]2\frac{3}{5}[/tex]In order to write it as a Decimal number, you need to divide the numerator 3 by the denominator 5 and then you must add the result to the Whole number 2. Therefore:
[tex]2\frac{3}{5}=2+0.6=2.6[/tex]Let be "c" the number of cups of flour that was used per pound.
Now you can set up the following proportion:
[tex]\frac{6.38}{2.6}=\frac{c}{1}[/tex]Solving for "c", you get:
[tex]\begin{gathered} \frac{6.38}{2.6}=c \\ \\ c=2.45 \end{gathered}[/tex]The answer is:
[tex]2.45\text{ }cups[/tex]