The National Center for Health Statistics reports the following age breakdown of deaths in the United States during 2002.

Age (Years)                             Number of Deaths (Thousands)
under 15.................................................................................. 40.01
15–under 25........................................................................... 33.08
25–under 35........................................................................... 41.38
35–under 45........................................................................... 91.01
45–under 55......................................................................... 172.21
55–under 65......................................................................... 253.73
65–under 75......................................................................... 424.11
75 or over........................................................................... 1391.99

Identify the following for the 45–under 55 class:

(a) frequency, 

(b) upper and lower limits, 

(c) width,

(d) midpoint.