Answer:
a) 20 minutes
b) 36 km/h
c) 33.67 km
d) continuous driving without any stationary phases.
Explanation:
by the way, speed is specified in distance per time unit. in your example as km/h. and that is how your write this.
not km/h¯¹. that would be wrong, as that would actually be km×h. but you can write e.g. km×h¯¹. that is the same as km/h.
between minutes 5 and 25 there is no progress in distance. so, for these 20 minutes the bus was stationary.
in the first 5 minutes the bus drove 7-4=3 km.
so, in 5 minutes 3 km. to determine the speed we need to calculate up to see, how many km would be have driven in a full hour (60 minutes). the same factor for the time has then to be applied also to the distance to keep the ratio unchanged.
5 × x = 60
x = 12
3 × 12 = 36
so, the speed in these first 5 minutes was 3 km/5 min.
or then in km/h : 36 km/h
between the minutes 25 and 45 the bus drove with a speed of 80km/h.
and the starting point there was at 7 km.
so, the bus drove s-7 km in 20 minutes.
as before, let's first find the scaling factor to deal with a full hour instead of only 20 minutes.
20 × x = 60
x = 3
as before : distance × scaling factor = distance for km/h
(s-7) × 3 = 80
3s - 21 = 80
3s = 101
s = 33.666666666... km