Finding the Fourth Proportional to 71.90, 99.32 and 57.18

Step by Step Solution

1. Step 1: Write the proportion equation
   71.90 : 99.32 = 57.18 : x
2. Step 2: Convert to fraction form
   71.90/99.32 = 57.18/x
3. Step 3: Cross multiply
   71.90x = 99.32 × 57.18
4. Step 4: Simplify right side
   71.90x = 5,678.83
5. Step 5: Solve for x
   x = 5,678.83/71.90
6. Step 6: Final answer
   x = 78.99