Finding the Fourth Proportional to 105.20, 145.07 and 90.50

Step by Step Solution

1. Step 1: Write the proportion equation
   105.20 : 145.07 = 90.50 : x
2. Step 2: Convert to fraction form
   105.20/145.07 = 90.50/x
3. Step 3: Cross multiply
   105.20x = 145.07 × 90.50
4. Step 4: Simplify right side
   105.20x = 13,128.33
5. Step 5: Solve for x
   x = 13,128.33/105.20
6. Step 6: Final answer
   x = 124.79