Finding the Fourth Proportional to 78.72, 118.09 and 42.18

Step by Step Solution

1. Step 1: Write the proportion equation
   78.72 : 118.09 = 42.18 : x
2. Step 2: Convert to fraction form
   78.72/118.09 = 42.18/x
3. Step 3: Cross multiply
   78.72x = 118.09 × 42.18
4. Step 4: Simplify right side
   78.72x = 4,981.04
5. Step 5: Solve for x
   x = 4,981.04/78.72
6. Step 6: Final answer
   x = 63.28