Finding the Fourth Proportional to 99.66, 149.31 and 86.10

Step by Step Solution

1. Step 1: Write the proportion equation
   99.66 : 149.31 = 86.10 : x
2. Step 2: Convert to fraction form
   99.66/149.31 = 86.10/x
3. Step 3: Cross multiply
   99.66x = 149.31 × 86.10
4. Step 4: Simplify right side
   99.66x = 12,855.59
5. Step 5: Solve for x
   x = 12,855.59/99.66
6. Step 6: Final answer
   x = 128.99