12cm is bigger than 98 mm. To get the answer, divide 98 by 10, because there are 10 millimeters in 1 centimeter, so to get 98 mm in cm, we need to find out how many groups of 10 will go into 98. Then, compare your answer to 12. If it is less than 12, then 98 mm is smaller than 12 cm, and if it is greater than 12, then 98 mm is larger than 12 cm.
98 / 10 = 9.8
9.8 < 12
Therefore, 98 millimeters is smaller than 12 centimeters.
Hope this helps!