Ini gimana ya caranya tolong

[tex]p {}^{2} = d {}^{2} + (R + r) {}^{2} \\ p {}^{2} = 20 {}^{2} + (9 + 6) {}^{2} \\ p {}^{2} = 20 {}^{2} + 15 {}^{2} \\ p {}^{2} = 400 + 225 \\ p {}^{2} = 625 \\ p = \sqrt{625} \\ p = 25 \: cm[/tex]

Jadi, jawabannya D.