Which relationship is a function?

Measures of the angle of r, 31 s (x+4) t (3x+9)

Ammonia molecules have three hydrogen atoms and one nitrogen atom.how many of each atom arein five molecules of ammonia

In the triangles, tr = ge and sr = fe. if = 3.2 ft, which is a possible measure of ? 1.6 ft 3.0 ft 3.2 ft 4.0 ft