Finding the Fourth Proportional to 28,111.72, 42,188.40 and 13,320.72

Step by Step Solution

1. Step 1: Write the proportion equation
   28,111.72 : 42,188.40 = 13,320.72 : x
2. Step 2: Convert to fraction form
   28,111.72/42,188.40 = 13,320.72/x
3. Step 3: Cross multiply
   28,111.72x = 42,188.40 × 13,320.72
4. Step 4: Simplify right side
   28,111.72x = 561,979,863.65
5. Step 5: Solve for x
   x = 561,979,863.65/28,111.72
6. Step 6: Final answer
   x = 19,990.95