Since the mean of Exam A is 300 and the standard deviation is 25, Aira scored 1 standard deviation above the mean. This means

To do equivalently well in Exam B, Aira must also obtain a score of 1 standard deviation above the mean of Exam B. Thus, add the standard deviation of 10 to the mean of 51.

Thus, she needs to have a score of 61 in Exam B.