Compute the right answer of the following question

Question- A purely competitive firm finds that the market price for its product is $20. It has a fixed cost of $100 and a variable cost of $10 per unit for the first 50 units and then $25 per unit for all successive units.

Part 1- Does price exceed average variable cost for the first 50 units?

Part 2- What about for the first 100 units?

Part 3- What is the marginal cost per unit for the first 50 units? $ per unit.

Part 4- What is the marginal cost for units 51 and higher? $ per unit for subsequent units.

Part 5- For each of the first 50 units, does MR exceed MC?

Part 6- What about for units 51 and higher?

Part 7- What output level will yield the largest possible profit for this purely competitive firm?

Part 8- Producing how many units will maximize profit.

I need help to evaluate the marginal cost per unit.