Wally, aged 65, purchases an annuity paying 400 per month as long as both he and his wife, aged 60, survive, with the first payment occurring immediately. If either dies, the benefit is reduced to 300 per month for the life of the survivor. Find the net single premium for this annuity given 4o — 10, 45 — 8.5 and (12) 60:65 == 11.7.