Finding the Fourth Proportional to 12,961.55, 17,870.57 and 8,478.20

Step by Step Solution

1. Step 1: Write the proportion equation
   12,961.55 : 17,870.57 = 8,478.20 : x
2. Step 2: Convert to fraction form
   12,961.55/17,870.57 = 8,478.20/x
3. Step 3: Cross multiply
   12,961.55x = 17,870.57 × 8,478.20
4. Step 4: Simplify right side
   12,961.55x = 151,510,134.83
5. Step 5: Solve for x
   x = 151,510,134.83/12,961.55
6. Step 6: Final answer
   x = 11,689.20