Complete the conversion factor below. \( \square \) square feet \( =1 \) square mile

\( 2 \overbrace { \frac { D = 12 } { | r = ? } } c = ? \)

\( \int x ^ { 3 } \sqrt { x ^ { 2 } - 25 } d x \)

The length of an insect in the picture is 7 cm and its real length is 12 mm , then the drawing scale \( =\ldots \ldots: \ldots \ldots \)

(iii) \( \left\{\begin{aligned} x_{1}-5 x_{2}-x_{3}+12 x_{4}-x_{5} & =-4 \\ -2 x_{1}+10 x_{2}+3 x_{3}-33 x_{4}+2 x_{5}+x_{6} & =4 \\ x_{3}-9 x_{4}+x_{5} & =8 \\ x_{1}-5 x_{2}+2 x_{3}-15 x_{4}+2 x_{5}+x_{6} & =14\end{aligned}\right. \)

b) \( \int_{-4}^{6}\left(3 x^{4}-5 x^{3}+13 x^{2}-9 x+6\right) d x \)