Finding the Fourth Proportional to 78.72, 118.08 and 42.60

Step by Step Solution

1. Step 1: Write the proportion equation
   78.72 : 118.08 = 42.60 : x
2. Step 2: Convert to fraction form
   78.72/118.08 = 42.60/x
3. Step 3: Cross multiply
   78.72x = 118.08 × 42.60
4. Step 4: Simplify right side
   78.72x = 5,030.21
5. Step 5: Solve for x
   x = 5,030.21/78.72
6. Step 6: Final answer
   x = 63.90