The perimeter of a triangle is equal to the sum of all the sides of the triangle.
A triangle has 3 sides so:
Perimeter = side 1 + side 2+ side 3
We have the values of the perimeter and two sides:
perimeter = 30x + 40
Side 1= 12x + 6
Side 2= 10x + 20
S3= ?
So, replacing with the values given:
30x+40= (12x+6)+(10x+20)+ S3
Solving for S3 ( side 3)
30x+40= 12x+6+10x+20+S3
30x+40=12x+10x+6+20+S3
30x+40= 22x+26+S3
30x+40-22x-26=S3
30x-22x+40-26=S3
8x+14 =S3
Lenght of the third side = 8x+14
