The following grouped data show the daily temperatures (in °C) recorded in a town:
20–24 : 3
25–29 : 7
30–34 : 5
35–39 : 1
A student plans to draw a histogram using a vertical scale of 1 cm = 2 observations. What should be the height of the rectangle for the class 25–29?
(a) 7 cm
(b) 3.5 cm
(c) 14 cm
(d) 5 cm