Finding the Fourth Proportional to 42,720.39, 64,086.71 and 13,140.72

Step by Step Solution

1. Step 1: Write the proportion equation
   42,720.39 : 64,086.71 = 13,140.72 : x
2. Step 2: Convert to fraction form
   42,720.39/64,086.71 = 13,140.72/x
3. Step 3: Cross multiply
   42,720.39x = 64,086.71 × 13,140.72
4. Step 4: Simplify right side
   42,720.39x = 842,145,335.19
5. Step 5: Solve for x
   x = 842,145,335.19/42,720.39
6. Step 6: Final answer
   x = 19,712.96