Finding the Fourth Proportional to 85.61, 128.61 and 78.99

Step by Step Solution

1. Step 1: Write the proportion equation
   85.61 : 128.61 = 78.99 : x
2. Step 2: Convert to fraction form
   85.61/128.61 = 78.99/x
3. Step 3: Cross multiply
   85.61x = 128.61 × 78.99
4. Step 4: Simplify right side
   85.61x = 10,158.90
5. Step 5: Solve for x
   x = 10,158.90/85.61
6. Step 6: Final answer
   x = 118.67