Finding the Fourth Proportional to 99.90, 149.72 and 54.18

Step by Step Solution

1. Step 1: Write the proportion equation
   99.90 : 149.72 = 54.18 : x
2. Step 2: Convert to fraction form
   99.90/149.72 = 54.18/x
3. Step 3: Cross multiply
   99.90x = 149.72 × 54.18
4. Step 4: Simplify right side
   99.90x = 8,111.83
5. Step 5: Solve for x
   x = 8,111.83/99.90
6. Step 6: Final answer
   x = 81.20