Finding the Fourth Proportional to 109.95, 164.71 and 85.78

Step by Step Solution

1. Step 1: Write the proportion equation
   109.95 : 164.71 = 85.78 : x
2. Step 2: Convert to fraction form
   109.95/164.71 = 85.78/x
3. Step 3: Cross multiply
   109.95x = 164.71 × 85.78
4. Step 4: Simplify right side
   109.95x = 14,128.82
5. Step 5: Solve for x
   x = 14,128.82/109.95
6. Step 6: Final answer
   x = 128.50