Finding the Fourth Proportional to 78.91, 118.21 and 42.79

Step by Step Solution

1. Step 1: Write the proportion equation
   78.91 : 118.21 = 42.79 : x
2. Step 2: Convert to fraction form
   78.91/118.21 = 42.79/x
3. Step 3: Cross multiply
   78.91x = 118.21 × 42.79
4. Step 4: Simplify right side
   78.91x = 5,058.21
5. Step 5: Solve for x
   x = 5,058.21/78.91
6. Step 6: Final answer
   x = 64.10