Using the data in RDCHEM, the following equation was obtained by OLS:

$=2\mathrm{.}613+0\mathrm{.}00300\mathrm{.}00000000702$

$(0\mathrm{.}429)(0\mathrm{.}00014)(0\mathrm{.}0000000037)$

n $=32,$ R$2=0\mathrm{.}1484.$

i$.$ At what point does the marginal effect of sales on rdintens become negative?

ii$.$ Would you keep the quadratic term in the model? Explain.