2012 AMC 8 Problem 9

The Fort Worth Zoo has a number of two-legged birds and a number of four-legged mammals. On one visit to the zoo, Margie counted 200 heads and 522 legs. How many of the animals that Margie counted were two-legged birds?

\textbf{(A)}\ 61\qquad\textbf{(B)}\ 122\qquad\textbf{(C)}\ 139\qquad\textbf{(D)}\ 150\qquad\textbf{(E)}\ 161

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.