Finding the Fourth Proportional to 91.31, 136.82 and 39.90

Step by Step Solution

1. Step 1: Write the proportion equation
   91.31 : 136.82 = 39.90 : x
2. Step 2: Convert to fraction form
   91.31/136.82 = 39.90/x
3. Step 3: Cross multiply
   91.31x = 136.82 × 39.90
4. Step 4: Simplify right side
   91.31x = 5,458.96
5. Step 5: Solve for x
   x = 5,458.96/91.31
6. Step 6: Final answer
   x = 59.78