for this question, the tolerance is telling us that the actual diameter of the engine is no more than 9.2 + 0.01 cm and now less than 9.2 - 0.01 cm.
Thus the range of values of the actual diameter is
9.19 cm - 9.21 cm
Another way of phrasing this is letting 'x' denote the actual value of the diameter and then limiting 'x' to being within 0.01 cm of 9.2:
|x - 9.2| <= 0.01
Which is identical to
-0.01 <= x - 9.2 <= 0.01
Or . . .
9.19 <= x <= 9.21
