Solution:
Let us denote by x the original amount (the money in her purse). According to the data of the problem if she adds 51 rs to the amount of money x in her purse, then the total of money becomes four times the original amount, that is:
Total money = 51+x = 4x
this is equivalent to:
3x= 51
solving for x, we get:
x = 51/3 = 17
So that, we can conclude that the correct answer is:
is the original amount in her purse is 17 rs.