Question

From 1990 to 1994, the mail order sales of
health products in the United States can be modeled by
S = 10t 3 + 115t 2 + 25t + 2505
where S is the sales (in millions of dollars) and t is the
number of years since 1990. In what year were about
$3885 million of health products sold? (Hint: First
substitute 3885 for S, then divide both sides by 5.)

Answer 1

I don't see why you don't follow their hint.
Try it.