Finding the Fourth Proportional to 89.78, 123.78 and 67.91

Step by Step Solution

1. Step 1: Write the proportion equation
   89.78 : 123.78 = 67.91 : x
2. Step 2: Convert to fraction form
   89.78/123.78 = 67.91/x
3. Step 3: Cross multiply
   89.78x = 123.78 × 67.91
4. Step 4: Simplify right side
   89.78x = 8,405.90
5. Step 5: Solve for x
   x = 8,405.90/89.78
6. Step 6: Final answer
   x = 93.63