Q1. Find all values of x (if any) where the tangent line to the graph of the given equation is horizontal. Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.

y=x+x1

X = __?____

Q2. The price per barrel of crude oil in the period 1980-2013, in constant 2014 dollars, can be approximated by

P(t) = 0.27t² 8.6t + 93 dollars (0 t 33),

where t is time in years since the start of 1980. Find P'(t) and P'(31).

P'(t) = _________

P'(31) = $ _______ per year

What does the second answer tell you about the price of crude oil? The price of a barrel of crude oil was increasing at a rate of $___?__ per year in ___?___.