Explanation:

Given % discount be 25% i.e. 25/100  = (1/4)^th part
As, marked price = 4
Then discount = 4 ×(1/4) = 1
Then cost of mobile = 4 − 1 = 3
As 3 ratio cost be 4875
∴ 1 ratio costs be  4875/ 3 = 1625
Thus, original price = (1625 × 4) = 6500