Finding the Fourth Proportional to 111.51, 153.90 and 78.75

Step by Step Solution

1. Step 1: Write the proportion equation
   111.51 : 153.90 = 78.75 : x
2. Step 2: Convert to fraction form
   111.51/153.90 = 78.75/x
3. Step 3: Cross multiply
   111.51x = 153.90 × 78.75
4. Step 4: Simplify right side
   111.51x = 12,119.63
5. Step 5: Solve for x
   x = 12,119.63/111.51
6. Step 6: Final answer
   x = 108.69