Finding the Fourth Proportional to 100.42, 138.72 and 80.98

Step by Step Solution

1. Step 1: Write the proportion equation
   100.42 : 138.72 = 80.98 : x
2. Step 2: Convert to fraction form
   100.42/138.72 = 80.98/x
3. Step 3: Cross multiply
   100.42x = 138.72 × 80.98
4. Step 4: Simplify right side
   100.42x = 11,233.55
5. Step 5: Solve for x
   x = 11,233.55/100.42
6. Step 6: Final answer
   x = 111.87