Finding the Fourth Proportional to 100.89, 139.08 and 78.69

Step by Step Solution

1. Step 1: Write the proportion equation
   100.89 : 139.08 = 78.69 : x
2. Step 2: Convert to fraction form
   100.89/139.08 = 78.69/x
3. Step 3: Cross multiply
   100.89x = 139.08 × 78.69
4. Step 4: Simplify right side
   100.89x = 10,943.51
5. Step 5: Solve for x
   x = 10,943.51/100.89
6. Step 6: Final answer
   x = 108.48