mam/sir it is c - a not c-d... reply..

Dear student

Log_ab =4  means a⁴=b

and log_cd =2  means c²=d

given b-d =7 so a⁴-c² =b-d=7

so (a-c)(a+c)(a²+c)=7

a and c are positive since log is not defined for negative values

So (a+c) and (a²+c) are positive

since  (a-c)(a+c)(a²+c) is positive  so a-c >0

So, c-a < 0  so option b is the correct answer