1 math question

14.
s is partly constant and partly varies inversely as t.
s = k1 + (k2/t)
where k1 and k2 are constant.

When t = 2, s = 7 :
7 = k1 + (k2/2) ...... [1]

When t = 4, s = 6 :
6 = k1 + (k2/4)
12 = 2k1 + (k2/2) ...... [2]

[2] - [1] :
k1 = 5

Put k1 = 5 into [1] :
7 = 5 + (k2/2)
k2/2 = 2
k2 = 4

Hence, s = 5 + (4/t)

When t = 1 :
s = 5 + (4/1)
s = 9