Finding the Fourth Proportional to 99.40, 137.21 and 78.72

Step by Step Solution

1. Step 1: Write the proportion equation
   99.40 : 137.21 = 78.72 : x
2. Step 2: Convert to fraction form
   99.40/137.21 = 78.72/x
3. Step 3: Cross multiply
   99.40x = 137.21 × 78.72
4. Step 4: Simplify right side
   99.40x = 10,801.17
5. Step 5: Solve for x
   x = 10,801.17/99.40
6. Step 6: Final answer
   x = 108.66