Finding the Fourth Proportional to 103.69, 142.09 and 99.91

Step by Step Solution

1. Step 1: Write the proportion equation
   103.69 : 142.09 = 99.91 : x
2. Step 2: Convert to fraction form
   103.69/142.09 = 99.91/x
3. Step 3: Cross multiply
   103.69x = 142.09 × 99.91
4. Step 4: Simplify right side
   103.69x = 14,196.21
5. Step 5: Solve for x
   x = 14,196.21/103.69
6. Step 6: Final answer
   x = 136.91