Since in the given recipe
7 1/2 cups of flour make 3 loaves of bread
We need to find the relation between f cups of flour to make b loaves of bread
[tex]\begin{gathered} 7\frac{1}{2}\colon3=f\colon b \\ \frac{7\frac{1}{2}}{3}=\frac{f}{b} \end{gathered}[/tex]By using the cross multiplication
[tex]\begin{gathered} 7\frac{1}{2}\times b=f\times3 \\ 7.5b=3f \end{gathered}[/tex]Divide both sides by 7.5
[tex]\begin{gathered} \frac{7.5b}{7.5}=\frac{3f}{7.5} \\ b=\frac{2}{5}f \end{gathered}[/tex]The equation which represents the relation between b and f is
[tex]b=\frac{2}{5}f[/tex]