Finding the Fourth Proportional to 128.63, 192.89 and 90.15

Step by Step Solution

1. Step 1: Write the proportion equation
   128.63 : 192.89 = 90.15 : x
2. Step 2: Convert to fraction form
   128.63/192.89 = 90.15/x
3. Step 3: Cross multiply
   128.63x = 192.89 × 90.15
4. Step 4: Simplify right side
   128.63x = 17,388.58
5. Step 5: Solve for x
   x = 17,388.58/128.63
6. Step 6: Final answer
   x = 135.19