Ken had the following problem on a quiz: Two sides of a triangle have lengths of 8 feet and 11 feet. If the triangle’s perimeter is 28 feet, what is the length of the third side? Ken solved the problem as shown below. P = a + b + c. 28 = 8 + 11 + c. 28 = 19 + c. 47 = c. Which statement about Ken’s work is true? Ken substituted into the formula incorrectly. Ken added incorrectly when combining like terms. Ken added 19 to both sides of the equation rather than subtracting 19. Ken solved the equation correctly.