Finding the Fourth Proportional to 112.42, 168.31 and 78

Step by Step Solution

1. Step 1: Write the proportion equation
   112.42 : 168.31 = 78 : x
2. Step 2: Convert to fraction form
   112.42/168.31 = 78/x
3. Step 3: Cross multiply
   112.42x = 168.31 × 78
4. Step 4: Simplify right side
   112.42x = 13,128.18
5. Step 5: Solve for x
   x = 13,128.18/112.42
6. Step 6: Final answer
   x = 116.78