Hey everyone! I'd greatly appreciate some thoughts on these problems. Thanks in advance.

2) Modeling Data. The manager of a store recorded the annual sale S (in thousand of dollars) of a product over a period of 7 years, as show in the table, where t is the time in years, with t = 1 corresponding to 1991.

t....(1)......(2)......(3)........(4).....(5)....( 6).....(7)

S...(5.4)..(6.9)....(11.5)...(15.5)..(19)...(22).. .(23.6)

I was supposed to find a cubic function regression function and I did. But then one part says:

Use calculus to find the time when sale were increasing at the greatest.
Does this mean find the absolute maximum?