Finding the Fourth Proportional to 111.51, 153.77 and 86.91

Step by Step Solution

1. Step 1: Write the proportion equation
   111.51 : 153.77 = 86.91 : x
2. Step 2: Convert to fraction form
   111.51/153.77 = 86.91/x
3. Step 3: Cross multiply
   111.51x = 153.77 × 86.91
4. Step 4: Simplify right side
   111.51x = 13,364.52
5. Step 5: Solve for x
   x = 13,364.52/111.51
6. Step 6: Final answer
   x = 119.85