The perimeter of the scalene triangle is 54. 6 cm. A scalene triangle where all sides are different lengths. The base of the triangle, labeled 3 a, is three times that of the shortest side, a. The other side is labeled b. Which equation can be used to find the value of b if side a measures 8. 7 cm? 8. 7 plus b equals 54. 6 17. 4 plus b equals 54. 6 26. 1 plus b equals 54. 6 34. 8 plus b equals 54. 6.