Finding the Fourth Proportional to 21,091.22, 29,111.66 and 13,128.72

Step by Step Solution

1. Step 1: Write the proportion equation
   21,091.22 : 29,111.66 = 13,128.72 : x
2. Step 2: Convert to fraction form
   21,091.22/29,111.66 = 13,128.72/x
3. Step 3: Cross multiply
   21,091.22x = 29,111.66 × 13,128.72
4. Step 4: Simplify right side
   21,091.22x = 382,198,832.88
5. Step 5: Solve for x
   x = 382,198,832.88/21,091.22
6. Step 6: Final answer
   x = 18,121.23