Throughout her career, an athlete has been timed in 120 of her 400-metre races. Her times, denoted by t seconds, were recorded on indoor tracks 45 times and are summarised by ­ Σ(t − 60) = 83.7, and on outdoor tracks where ­Σ(t − 65) = −38.7. Calculate her average 400-metre running time and comment on the accuracy of your answer.