Finding the Fourth Proportional to 90.86, 135.69 and 86.18

Step by Step Solution

1. Step 1: Write the proportion equation
   90.86 : 135.69 = 86.18 : x
2. Step 2: Convert to fraction form
   90.86/135.69 = 86.18/x
3. Step 3: Cross multiply
   90.86x = 135.69 × 86.18
4. Step 4: Simplify right side
   90.86x = 11,693.33
5. Step 5: Solve for x
   x = 11,693.33/90.86
6. Step 6: Final answer
   x = 128.70