Finding the Fourth Proportional to 91.98, 138.45 and 78.78

Step by Step Solution

1. Step 1: Write the proportion equation
   91.98 : 138.45 = 78.78 : x
2. Step 2: Convert to fraction form
   91.98/138.45 = 78.78/x
3. Step 3: Cross multiply
   91.98x = 138.45 × 78.78
4. Step 4: Simplify right side
   91.98x = 10,907.91
5. Step 5: Solve for x
   x = 10,907.91/91.98
6. Step 6: Final answer
   x = 118.59