Finding the Fourth Proportional to 91.63, 138.11 and 90.72

Step by Step Solution

1. Step 1: Write the proportion equation
   91.63 : 138.11 = 90.72 : x
2. Step 2: Convert to fraction form
   91.63/138.11 = 90.72/x
3. Step 3: Cross multiply
   91.63x = 138.11 × 90.72
4. Step 4: Simplify right side
   91.63x = 12,528.89
5. Step 5: Solve for x
   x = 12,528.89/91.63
6. Step 6: Final answer
   x = 136.73