I have 2 similar questions regarding quadratic (2nd order) and cubic (third
order) polynomial curve fits.

Dataset 1 is comprised of the following (x,y) pairs: (5, 0.02305), (8,
0.03235), (12, 0.04655), (16, 0.07065), (20, 0.09195), (24,0.11935), (32,
0.17605) and (40,0.24485). After X-Y scatter, the resulting polynomial
equation results: y= 8E-05x^2 + 0.002X + 0.006. I have a variety of addtional
Y, for which I must solve for X using the quadratic formula- everything I try
works on the linear model, which is unacceptable.

Dataset 2 is comprised of the following (x,y) pairs: (0, 0.2795), (1,
0.2947), (2, 0.3113), (5, 0.3697), (10, 0.4756), (20, 0.6772), (60, 0.9729)
and (100, 1.6345). After X-Y scatter, the resulting polynomial equation
results: y= 3E-06x^3 - 0.000x^2 + 0.027X + 0.262. I have a variety of
addtional Y, for which I must solve for X using the cubic formula- everything
I try works on the linear model, which is unacceptable.