Finding the Fourth Proportional to 172.17, 258.72 and 91.05

Step by Step Solution

1. Step 1: Write the proportion equation
   172.17 : 258.72 = 91.05 : x
2. Step 2: Convert to fraction form
   172.17/258.72 = 91.05/x
3. Step 3: Cross multiply
   172.17x = 258.72 × 91.05
4. Step 4: Simplify right side
   172.17x = 23,556.46
5. Step 5: Solve for x
   x = 23,556.46/172.17
6. Step 6: Final answer
   x = 136.82