The bond interest rate risk is affected by coupon rate as well as maturity period. Other things keeping equal the bond with lower coupon rate would have higher interest rate risk, similarly other things keeping equal the bond with longer maturity period will have higher interest rate risk. Here when Amy says that Bond A has higher interest rate risk because bond A has lower coupon rate so she might be correctly saying that if we keep the other things constant. Similarly, when Bob says that bond B has greater interest rate risk because its maturity period is higher than Bond A, Bob can also be true if we keep the other things constant. Here the logic applied by both of them is correct but in order to decide which bond has higher interest rate risk we need to calculate the duration of the bond and given the duration is also dependent on the maturity period, there is high probability that Bond B is more interest rate sensitive than bond A, but in order to be sure we should calculate the duration of the bond.