Finding the Fourth Proportional to 100.72, 139.01 and 61.40

Step by Step Solution

1. Step 1: Write the proportion equation
   100.72 : 139.01 = 61.40 : x
2. Step 2: Convert to fraction form
   100.72/139.01 = 61.40/x
3. Step 3: Cross multiply
   100.72x = 139.01 × 61.40
4. Step 4: Simplify right side
   100.72x = 8,534.91
5. Step 5: Solve for x
   x = 8,534.91/100.72
6. Step 6: Final answer
   x = 84.74