Answer:
350 the number of pretzels that must be sold to maximize profit.
Step-by-step explanation:
P(x) = -0.002x2 + 1.4x - 400
Differentiating P(x) with respect to dx:


Putting , P(x)' =0


we get , x = 350
Differentiating P(x)' with respect to dx:

P(x)''<0 (maxima)
350 the number of pretzels that must be sold to maximize profit.