Finding the Fourth Proportional to 31,087.74, 42,907.71 and 20,478.30

Step by Step Solution

1. Step 1: Write the proportion equation
   31,087.74 : 42,907.71 = 20,478.30 : x
2. Step 2: Convert to fraction form
   31,087.74/42,907.71 = 20,478.30/x
3. Step 3: Cross multiply
   31,087.74x = 42,907.71 × 20,478.30
4. Step 4: Simplify right side
   31,087.74x = 878,676,957.69
5. Step 5: Solve for x
   x = 878,676,957.69/31,087.74
6. Step 6: Final answer
   x = 28,264.42