Find the directional derivative of f(x, y,z)=xy+z3f(x, y,z)=xy+z3 at the point (3,2,1)(3,2,1) in the direction of a vector making an angle of 3π43π4 with ∇f(3,2,1)∇f(3,2,1).

Adan has decided to purchase an $9000 car. he plans on putting 20% down toward the purchase and financing the rest at 7.9% interest rate for 3 years. find his monthly payment a) $225.29 b) $298.81 c) $204.78 d) $236.89