Total of the 10 numbers = 10 × 12 = 120.<br><br>
Sum of the three removed numbers = 5 + 15 + 20 = 40.<br>
Remaining sum after removal = 120 − 40 = 80.<br>
Number of values becomes 10 − 3 + 1 = 8.<br><br>
New average = 13, so 80 + x = 8 × 13 = 104.<br>
x = 104 − 80 = 24.<br><br>
Final Answer: 24