Respuesta :

3x - 7

The perimeter is the sum of all 3 sides of the triangle

To find the third side subtract the sum of the 2 known sides from the perimeter

x + 3 + 2x + 4 = 3x + 7

third side = 6x - (3x + 7 ) = 6x - 3x - 7 = 3x - 7