Finding the Fourth Proportional to 100.78, 139.05 and 59.31

Step by Step Solution

1. Step 1: Write the proportion equation
   100.78 : 139.05 = 59.31 : x
2. Step 2: Convert to fraction form
   100.78/139.05 = 59.31/x
3. Step 3: Cross multiply
   100.78x = 139.05 × 59.31
4. Step 4: Simplify right side
   100.78x = 8,247.06
5. Step 5: Solve for x
   x = 8,247.06/100.78
6. Step 6: Final answer
   x = 81.83