Finding the Fourth Proportional to 86.21, 129.34 and 42.88

Step by Step Solution

1. Step 1: Write the proportion equation
   86.21 : 129.34 = 42.88 : x
2. Step 2: Convert to fraction form
   86.21/129.34 = 42.88/x
3. Step 3: Cross multiply
   86.21x = 129.34 × 42.88
4. Step 4: Simplify right side
   86.21x = 5,545.45
5. Step 5: Solve for x
   x = 5,545.45/86.21
6. Step 6: Final answer
   x = 64.32