Carl's Triangle has dimensions of Base/opposite = 4 and Height/Adjacent = 3. Diagonal/Hypotenuse = x. Using the Pythagorean theorem X^2 = Base^2 + Height^2.
Thus X = Sqrt√(B^2 + Height^2)
X= √(4^2+3^)
X= √(16+9)
X= ✓(25)
X=5
Perimeter of Triangle = 5+4+3 = 12 inch.