The compound interest formula is
[tex]A=P\cdot(1+r)^t[/tex]In the exercise, we have:
A=2800
P=2200
t=7
[tex]\begin{gathered} A=P(1+r)^t \\ 2800=2200(1+r)^7 \\ \frac{2800}{2200}=(1+r)^7 \\ \frac{14}{11}=(1+r)^7 \\ \sqrt[7]{\frac{14}{11}}=\sqrt[7]{(1+r)^7} \\ \sqrt[7]{\frac{14}{11}}=1+r \\ 1.0351=1+r \\ r=1.0351-1 \\ r=0.0351 \\ r=0.04 \end{gathered}[/tex]Answer: 3.51%
