Water in an electric kettle connected to a 220V supply takes 6.5 min to reach its boiling point.How

Let 'r' be the resistance of the electric kettle, v1= 22o v , t1 = 6.5 min , v2= 200 v , t2 = ?
As the heat produced in both the cases will be same ,
Use the relation,
heat produced = v12 t1 / r = v22 t2 / r
and plug in the values , to get the time t2, required if the supply had been 200V .