Finding the Fourth Proportional to 99.61, 137.60 and 78.91

Step by Step Solution

1. Step 1: Write the proportion equation
   99.61 : 137.60 = 78.91 : x
2. Step 2: Convert to fraction form
   99.61/137.60 = 78.91/x
3. Step 3: Cross multiply
   99.61x = 137.60 × 78.91
4. Step 4: Simplify right side
   99.61x = 10,858.02
5. Step 5: Solve for x
   x = 10,858.02/99.61
6. Step 6: Final answer
   x = 109.01