Each lion has 1 head. The number of lion heads is L .
Each bird has 1 head. The number of bird heads is B.
The total number of heads of all species is (L + B) = 30
Each lion has 4 feet. The number of lion feet is 4L .
Each bird has 2 feet. The number of bird feet is 2B .
The total number of feet of all species is (4L + 2B) = 100
The system of linear equations is:
L + B = 30
4L + 2B = 100 .