Added Solution for Github-Externship-Assignment

[yogeshguptakaithal]

Appraoch-
1)Firstly find position of '?' i.e. whether ? is in first number , second, third or fourth
2)Now try four cases accoding to possible postions of '?'.
if'?' is in A then our needed A should be (D-C)/B and then compare this with the string of A given in Q and return the needed digit
if'?' is in B then our needed B should be (D-C)/A and then compare this with the string of A given in Q and return the needed digit
if'?' is in C then our needed C should be D-(AB) and then compare this with the string of A given in Q and return the needed digit
if'?' is in D then our needed D should be AB+C and then compare this with the string of A given in Q and return the needed digit