Finding the Fourth Proportional to 139.10, 191.43 and 128.72

Step by Step Solution

1. Step 1: Write the proportion equation
   139.10 : 191.43 = 128.72 : x
2. Step 2: Convert to fraction form
   139.10/191.43 = 128.72/x
3. Step 3: Cross multiply
   139.10x = 191.43 × 128.72
4. Step 4: Simplify right side
   139.10x = 24,641.35
5. Step 5: Solve for x
   x = 24,641.35/139.10
6. Step 6: Final answer
   x = 177.15