The radius of a circle is doubled a. how does the circumference change? b. how does the area change?

The function a represents the cost of manufacturing product a, in hundreds of dollars, and the function b represents the cost of manufacturing product b, in hundreds of dollars. a(t) = 5t + 2 b(t) = 7t - 2t +4 find the expression that describes the total cost of manufacturing both products, a(t) + b(t). a. 7t^2 - 7t + 2 b. 7t^2 + 3 +6 c. 7t^2 + 7t - 6 d. 7t^2 - 3t + 6

Can you me find the missing length. i attached an image.

8. kelly wants to buy a magazine that is $25. later the magazine was marked up an additional 20%. what is the new price?