if interest on rs1500 be more than interest on rs1200 by rs90 in 6yrs.find rate%
since the time is 6 years, I will assume you are using compound interest, simple interest normally would not be used for that length of time
Let the interest rate be i
1500(1+i)^6 - 1200(1+i)^6 = 90
isolate (1+i)^6
take the 6th root of both sides and you have it