Notice that the first figure consists of 3 squares, the second one of 5 squares, the third one of 7 squares, and the fourth one of 9 squares. Furthermore,
[tex]\begin{gathered} f_1=3=3+2(0) \\ f_2=5=3+2(1) \\ f_3=7=3+2(2) \\ f_4=9=3+2(3) \\ \Rightarrow f_n=3+2(n-1) \end{gathered}[/tex]
Using this rule, set n=10 and we obtain
[tex]f_{10}=3+2(10-1)=3+2(9)=3+18=21[/tex]
Then, the answer is 21, option G
