Use the distance formula to find the length of the sides and sum them up
[tex]|PO|= \sqrt{(7 - - 2) {}^{2} + ( - 3 - 9) {}^{2} } [/tex]
[tex]|PO|= \sqrt{(7 + 2) {}^{2} + ( -3 - 9) {}^{2} } [/tex]
[tex]|PO|= \sqrt{(9) {}^{2} + ( - 12) {}^{2} } [/tex]
[tex]|PO|= \sqrt{81+ 144 } [/tex]
[tex]|PO| = \sqrt{225} [/tex]
[tex]|PO| = 15 \: units[/tex]
Also,
[tex]|PR|=\sqrt{( - 2 + 2) {}^{2} + ( - 3 - 9) {}^{2} } [/tex]
[tex]|PR|=\sqrt{( 0) {}^{2} + ( - 12) {}^{2} } [/tex]
[tex]|PR|=\sqrt{0+ 144 } [/tex]
[tex]|PR| = \sqrt{144} [/tex]
[tex]|PR|=12 \: units[/tex]
And
[tex]|OR|=\sqrt{( - 2 - 7) {}^{2} + ( - 3 + 3) {}^{2} } [/tex]
[tex]|OR|=\sqrt{( - 9) {}^{2} + ( 0) {}^{2} } [/tex]
[tex]|OR|=\sqrt{0+ 81 } [/tex]
[tex]|OR|=\sqrt{81} [/tex]
[tex]|OR|=9 \: units[/tex]
Hence perimeter triangle POR
[tex] = 15 + 12 + 9[/tex]
[tex] = 36 \: units[/tex]