Answer with step-by-step explanation:
We are given that a function
Differentiate partially w.r.t x
Then, we get
Differentiate again w.r.t x
Differentiate function w.r.t y
Again differentiate w.r.t y
Differentiate partially w.r.t y
Hence, if f(x,y) is of class 
(is twice continuously differentiable), then the mixed partial derivatives are equal.
i.e
Answer:
answer to the question is B
9.89%
You can get this number by multiplying the two together.
23 regular coffees were served.
25% means 1/4
25% x 92 = 23 regular coffees were served.
92 - 23 = 69 decaf coffees were served.
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