HELP Please I HAVE bad grades!

Kayla made observations about the sellin price of a new brand of coffee that sold in the three different sized bags she recorded those observations in the following table 6 is $2.10 8 is $2.80 and 16 is to $5.60 use the relationship to predict the cost of a 20oz bag of coffee.

Find the condition that the zeros of the polynomial f(x) = x^3+3px^2+3px+r may be in a.p.

Could someone me with this question i’ve been stuck on it for 20 minutes