Hello, I have a homework from economics which is probably quite simple, but i just can't think of the next step The task is: The costs of a firm are...

Hello,

I have a homework from economics which is probably quite simple, but i just can't think of the next step

The task is: The costs of a firm are determined by the function AC = q2 - 6q + 70.

a) From what number of output will there start to be diminishing returns from variable input?

b) From what number of input does a firm reach the point of shutdown?

I know that the shutdown point will be a point where the revenue is lower than variable cost.

I will appreciate some help, as I feel that it shouldn't be too complicated but I feel like I would need to know AVC and AFC or MC to get the result. How do I get them from just AC (some people also use ATC).

Have a good day!