Finding the Fourth Proportional to 128.81, 177.86 and 99.86

Step by Step Solution

1. Step 1: Write the proportion equation
   128.81 : 177.86 = 99.86 : x
2. Step 2: Convert to fraction form
   128.81/177.86 = 99.86/x
3. Step 3: Cross multiply
   128.81x = 177.86 × 99.86
4. Step 4: Simplify right side
   128.81x = 17,760.46
5. Step 5: Solve for x
   x = 17,760.46/128.81
6. Step 6: Final answer
   x = 137.88