Answer:
Perimeter of the Triangle
[tex]( {x}^{2} - 5x + 13) + (2 {x}^{2} - x + 19) + ( {x}^{2} + 3x + 21) \\ =(1 + 2 + 1) {x}^{2} + ( - 5 - 1 + 3)x + (13 + 19 + 21) \\ =(4 {x}^{2} - 3x + 53) \: units[/tex]
