If TC= 400 + 30Q + 5Q, what is the marginal cost at the 20 th unit? Assume P = 90 - 2Q and TC = 20 + Q, what level of production maximizes profit?

If TC= 400 + 30Q + 5Q², what is the marginal cost at the 20th unit?

Assume P = 90 – 2Q and TC = 20 + Q², what level of production maximizes profit?

A good’s demand is given by: P = 400 – 2Q. At P = 300, the point price elasticity is:

I need step by step how to solve these problems. Thanks.