Finding the Fourth Proportional to 128.79, 193.20 and 42.10

Step by Step Solution

1. Step 1: Write the proportion equation
   128.79 : 193.20 = 42.10 : x
2. Step 2: Convert to fraction form
   128.79/193.20 = 42.10/x
3. Step 3: Cross multiply
   128.79x = 193.20 × 42.10
4. Step 4: Simplify right side
   128.79x = 8,133.72
5. Step 5: Solve for x
   x = 8,133.72/128.79
6. Step 6: Final answer
   x = 63.15