First you have to figure out the area of the pool and the path together:
(20m + 2m)*(16m + 2m) = 22m * 18m = 396m^2
When you now subtract the area of the pool from the whole area, you'll get the area of the path:
396m^2 - (20m * 16m) = 396m^2 - 320m^2 = 76m^2 => area of the path
Next step is to figure out the area of one tile:
0,1m * 0,08m = 0,08m^2
Last step is to figure out, how many tiles fit in 76m^2:
76m^2 / 0,08m^2 = 950
costs: 950 * Rs 5 = Rs 4750
