Finding the Fourth Proportional to 78.90, 118.34 and 42.80

Step by Step Solution

1. Step 1: Write the proportion equation
   78.90 : 118.34 = 42.80 : x
2. Step 2: Convert to fraction form
   78.90/118.34 = 42.80/x
3. Step 3: Cross multiply
   78.90x = 118.34 × 42.80
4. Step 4: Simplify right side
   78.90x = 5,064.95
5. Step 5: Solve for x
   x = 5,064.95/78.90
6. Step 6: Final answer
   x = 64.19