plz answer this question..plzz

Answer:
[tex]Side\ 3 = 5p^2q + 3r[/tex]
Step-by-step explanation:
Given
[tex]Perimeter = 7p^2q + 13r[/tex]
[tex]Side\ 1 = 14r[/tex]
[tex]Side\ 2 = 2p^2q - 4r[/tex]
Required
Find the length of the third side
Perimeter is calculated as thus:
[tex]Perimeter = Side\ 1 + Side\ 2 + Side\ 3[/tex]
This gives:
[tex]7p^2q + 13r = 14r + 2p^2q - 4r + Side\ 3[/tex]
Collect like terms
[tex]Side\ 3 = 7p^2q - 2p^2q + 13r - 14r + 4r[/tex]
[tex]Side\ 3 = 5p^2q + 3r[/tex]