Weekly savings of Ramkali is following :
5, 6.75, 8.50, 10.25............
Here, a = 5, d = 1.75, Tn = 20.75
We know that, Tn = a + (n - 1) d 20.75 = 5 + (n - 1) (1.75)
20.72= 5 + 1.75 n - 1.75
20.75 = 1.7n + 3.25
1.75n = 17.5
Hence, n = 10.