Finding the Fourth Proportional to 91.28, 137.41 and 78.72

Step by Step Solution

1. Step 1: Write the proportion equation
   91.28 : 137.41 = 78.72 : x
2. Step 2: Convert to fraction form
   91.28/137.41 = 78.72/x
3. Step 3: Cross multiply
   91.28x = 137.41 × 78.72
4. Step 4: Simplify right side
   91.28x = 10,817.53
5. Step 5: Solve for x
   x = 10,817.53/91.28
6. Step 6: Final answer
   x = 118.51