Finding the Fourth Proportional to 78.63, 107.85 and 72.15

Step by Step Solution

1. Step 1: Write the proportion equation
   78.63 : 107.85 = 72.15 : x
2. Step 2: Convert to fraction form
   78.63/107.85 = 72.15/x
3. Step 3: Cross multiply
   78.63x = 107.85 × 72.15
4. Step 4: Simplify right side
   78.63x = 7,781.38
5. Step 5: Solve for x
   x = 7,781.38/78.63
6. Step 6: Final answer
   x = 98.96