Finding the Fourth Proportional to 100.78, 150.46 and 86.34

Step by Step Solution

1. Step 1: Write the proportion equation
   100.78 : 150.46 = 86.34 : x
2. Step 2: Convert to fraction form
   100.78/150.46 = 86.34/x
3. Step 3: Cross multiply
   100.78x = 150.46 × 86.34
4. Step 4: Simplify right side
   100.78x = 12,990.72
5. Step 5: Solve for x
   x = 12,990.72/100.78
6. Step 6: Final answer
   x = 128.90