Upper and lower bounds have two definitions, the upper bound can be the value that is equal or higher to the highest value in a set, an the lower bound is a value that is equal or smaller, but i believe your question doesnt deal with sets but rather the rounding number.
In Rounding numbers the Upper bound is the highest possible value that would still round off to be the value questioned, and vise versa the lowest value that could be rounded to be the same value is the lower bound.
1) If the length of the table is 200 cm, then rounding off to the nearest cm the difference can at most be 0.5 cm, meaning the lower bound would be 199.5 cm and the upper bound would be at most 200.5 cm [a bit smaller]
So the Upper Bound Is 200.5 cm | Lower bound is 199.5 cm
2) a-c /b comes out to (4.3-2.1) / 1 , a-c comes out as 2.2 which contains 2 significant numbers where as 1 as in B contains 1 significant number, when dividing/multiplyng we consider numbers to the smallest amount of significant numbers meaning 2.2/1 is 2 to 1 significant number , the lower bound being 1.5 and the upper bound being 2.5
3) Emily was born weighing 3 kg, 3 months in she was 6 kg, Emily had gained 3 kgs, the upper bound of the weight Emily had gained was 3.5 kg
4) If a case weighed 4 kg, 12 of these cases would weigh 48 kgs, thus the upper bound of this weight would be 48.5 kg
