If two sides of a triangle are 5 and 7 inches longer than the third side and the perimeter measures 21, find the length of each side of the triangle

hello

x
x +5 
x + 7

x + x + 5 + x + 7 = 21 
3 x = 21 - 12
3 x = 9
x = 3 

3 , 5 et 7 pouces