1) 10

Fixed costs are equal to total cost at output level 0 which in this case is 10.

2) 6

The marginal cost for the first unit of output is given in the marginal cost columns at output level 1 which is 6.

3)20

Total cost at 2 units of output is equal to total cost at 1 unit of output plus marginal cost at 2 units of output which is 16+4=20

4)10

Total variable costs at 2 units of output is the sum of marginal costs at or below 2 units of output which is 6+4=10

5)2

The marginal cost of the third unit of output is the difference between total variable costs between output levels 2 and 3 which is 12-10=2