What is the measure if angle A

99 points at a zoo, the leopard pen has a ring-shaped sidewalk around it. the outer edge of the sidewalk is a circle with a radius of 12 m. the inner edge of the sidewalk is a circle with a radius of 8 m. (1 point for showing all of your work) a. write and simplify an expression for the exact area of the sidewalk. (1 point for the answer) b. find the approximate area of the sidewalk. use 3.14 to approximate π. (1 point for the answer)

What are the measures of ∠a, ∠b, ∠c and ∠d? explain how to find each of the angles. measure need asap

Consider the reaction 2x2y2+z2⇌2x2y2z which has a rate law of rate= k[x2y2][z2] select a possible mechanism for the reaction.