Finding the Fourth Proportional to 91.46, 136.89 and 78.64

Step by Step Solution

1. Step 1: Write the proportion equation
   91.46 : 136.89 = 78.64 : x
2. Step 2: Convert to fraction form
   91.46/136.89 = 78.64/x
3. Step 3: Cross multiply
   91.46x = 136.89 × 78.64
4. Step 4: Simplify right side
   91.46x = 10,764.69
5. Step 5: Solve for x
   x = 10,764.69/91.46
6. Step 6: Final answer
   x = 117.70