Finding the Fourth Proportional to 99.87, 137.64 and 78.09

Step by Step Solution

1. Step 1: Write the proportion equation
   99.87 : 137.64 = 78.09 : x
2. Step 2: Convert to fraction form
   99.87/137.64 = 78.09/x
3. Step 3: Cross multiply
   99.87x = 137.64 × 78.09
4. Step 4: Simplify right side
   99.87x = 10,748.31
5. Step 5: Solve for x
   x = 10,748.31/99.87
6. Step 6: Final answer
   x = 107.62