Finding the Fourth Proportional to 91.80, 138.42 and 78.42

Step by Step Solution

1. Step 1: Write the proportion equation
   91.80 : 138.42 = 78.42 : x
2. Step 2: Convert to fraction form
   91.80/138.42 = 78.42/x
3. Step 3: Cross multiply
   91.80x = 138.42 × 78.42
4. Step 4: Simplify right side
   91.80x = 10,854.90
5. Step 5: Solve for x
   x = 10,854.90/91.80
6. Step 6: Final answer
   x = 118.25