Finding the Fourth Proportional to 99.78, 137.59 and 77.91

Step by Step Solution

1. Step 1: Write the proportion equation
   99.78 : 137.59 = 77.91 : x
2. Step 2: Convert to fraction form
   99.78/137.59 = 77.91/x
3. Step 3: Cross multiply
   99.78x = 137.59 × 77.91
4. Step 4: Simplify right side
   99.78x = 10,719.64
5. Step 5: Solve for x
   x = 10,719.64/99.78
6. Step 6: Final answer
   x = 107.43