Apples cost $3.60 for 3 pounds . The rate can be calculated as follows
[tex]\begin{gathered} 3\text{ pounds = \$3.60} \\ 1\text{ pounds = ?} \\ \text{rate = }\frac{3.60}{3} \\ \text{rate}=\text{ \$1.2 per pound} \end{gathered}[/tex]The amount of pounds you can buy for $8.40 can be computed below
[tex]\begin{gathered} \text{rate}=\frac{8.40}{\text{pounds}} \\ 1.2=\frac{8.40}{\text{pounds}} \\ weight\text{ in pounds = }\frac{8.40}{1.2} \\ \text{weight in pounds = 7 Ib} \end{gathered}[/tex]