Answer:
a)     $360,000
b)     $52,000
c) Net Income                             360,000            344,000        316,000
Explanation:
Part 1) Determine the net income for 2020 as follows using the First In First Out (FIFO)
= FIFO 2020 = $450,000 - The Income Tax
= $450,000 - ($450,000 x 0.35)
= $450,000- $90,000
= $360,000
Part 2) Compute the cumulative effect in change of the weighted average to FIFO
  Weighted average  FIFO    Difference    [email protected]%(difference)  net effect
2018  370,000               395,000    25,000                     5,000           20,000
2019   390,000              430,000     40,000                    8,000           32,000
Total in Net effect                                                                               $52,000
Part 3) Show comparative income statement as follows
                                                          2020                     2019                2018
Income before tax                          450,000              430,000         395,000
Remove the tax (@20)                      90,000                86,000          79,000
Net Income                                       360,000            344,000        316,000