A tree s size is a function of its alive. Size(___) s(___)

  0, 15); y equals one over sixty times x squared plus 15

Step-by-step explanation:

Assuming the halfpipe is only useful if the curve opens upward, the "base" (vertex) must be below the focus, so cannot be at (0, 60).

Apparently, the ground is supposed to be the directrix of the curve. Then the vertex is halfway between the focus and the ground, so is at (0, 15). The focus-vertex distance (p) is then 30-15 = 15, so the coefficient of the squared term is 1/(4p) = 1/(4·15) = 1/60.

For a vertex of (0, 15) and a vertical scale factor of 1/60, the equation of the curve is ...

  y = (1/60)x^2 +15 . . . . matches the last choice