Finding the Fourth Proportional to 90.72, 137.16 and 86.31

Step by Step Solution

1. Step 1: Write the proportion equation
   90.72 : 137.16 = 86.31 : x
2. Step 2: Convert to fraction form
   90.72/137.16 = 86.31/x
3. Step 3: Cross multiply
   90.72x = 137.16 × 86.31
4. Step 4: Simplify right side
   90.72x = 11,838.28
5. Step 5: Solve for x
   x = 11,838.28/90.72
6. Step 6: Final answer
   x = 130.49