Finding the Fourth Proportional to 99.99, 149.31 and 86.31

Step by Step Solution

1. Step 1: Write the proportion equation
   99.99 : 149.31 = 86.31 : x
2. Step 2: Convert to fraction form
   99.99/149.31 = 86.31/x
3. Step 3: Cross multiply
   99.99x = 149.31 × 86.31
4. Step 4: Simplify right side
   99.99x = 12,886.95
5. Step 5: Solve for x
   x = 12,886.95/99.99
6. Step 6: Final answer
   x = 128.88