Finding the Fourth Proportional to 91.98, 138.72 and 90.60

Step by Step Solution

1. Step 1: Write the proportion equation
   91.98 : 138.72 = 90.60 : x
2. Step 2: Convert to fraction form
   91.98/138.72 = 90.60/x
3. Step 3: Cross multiply
   91.98x = 138.72 × 90.60
4. Step 4: Simplify right side
   91.98x = 12,568.03
5. Step 5: Solve for x
   x = 12,568.03/91.98
6. Step 6: Final answer
   x = 136.64