Finding the Fourth Proportional to 100.50, 138.61 and 78.63

Step by Step Solution

1. Step 1: Write the proportion equation
   100.50 : 138.61 = 78.63 : x
2. Step 2: Convert to fraction form
   100.50/138.61 = 78.63/x
3. Step 3: Cross multiply
   100.50x = 138.61 × 78.63
4. Step 4: Simplify right side
   100.50x = 10,898.48
5. Step 5: Solve for x
   x = 10,898.48/100.50
6. Step 6: Final answer
   x = 108.45