return a value from one column based on value in another column

Consider the following:

A1 = M
A2 = N
A3 = P
A4 = Q

B1 = 5
B2 = 6
B3 = 7
B4 = 8

How do I search Column A for "N" (A2), then return the corresponding value in Column B, i.e. "6" (B2)?