Finding the Fourth Proportional to 111.31, 166.78 and 90.99

Step by Step Solution

1. Step 1: Write the proportion equation
   111.31 : 166.78 = 90.99 : x
2. Step 2: Convert to fraction form
   111.31/166.78 = 90.99/x
3. Step 3: Cross multiply
   111.31x = 166.78 × 90.99
4. Step 4: Simplify right side
   111.31x = 15,175.31
5. Step 5: Solve for x
   x = 15,175.31/111.31
6. Step 6: Final answer
   x = 136.33