The perimeter of a figure is the sum os the length of the sides of the figure. In this case, you have algebraic expressions for the length of the sides, then, sum the given expressions, as follow:
p = (c + 6) + (c + 6) + (c + 7)
cancel out parentheses:
p = c + 6 + c + 6 + c + 7
simplify like terms:
p = c + c + c + 6 + 6 + 7
p = 3c + 19
Hence, the perimeter of the given figure is 3c + 19