maths (Q)

The following table shows the changes in the Air pollution index (API) in
Causeway Bay or one day.Each change is calculated by subtracting the
reading at the previous hour from the present reading,e.g.the API at 4pm
was higher than that 3pm by 1 unit.

3pm 4pm 5pm 6pm 7pm 8pm
0 +1 -1 -1 -3 -3

(a)If the API at 2pm was 92 unit,find the API at 8pm
(b)If the API at 7pm was 100 unit,find the API at 3pm