Well, the bigger side equals 6, that we can see from the graph, also, the smaller side equals 3, which we can also see on the graph. There is a right angle between these two sides, so we can use the Pythagorean theorem to find the hypotenuse c:
c^2 = 6^2 + 3^2
c^2 = 36 + 9
c^2 = 45
c = square root of 45 = approximately 6,7
Then the perimeter = 6 + 3 + 6,7 = 15,7
The answer is C) approximately 15,7 units