Finding the Fourth Proportional to 91.58, 136.78 and 78.77

Step by Step Solution

1. Step 1: Write the proportion equation
   91.58 : 136.78 = 78.77 : x
2. Step 2: Convert to fraction form
   91.58/136.78 = 78.77/x
3. Step 3: Cross multiply
   91.58x = 136.78 × 78.77
4. Step 4: Simplify right side
   91.58x = 10,774.31
5. Step 5: Solve for x
   x = 10,774.31/91.58
6. Step 6: Final answer
   x = 117.66