Jeff, a single taxpayer, operates a bicycle shop. For the calendar year 2017 he reports the following items of income and expense:

Gross income from business. . . . . . . . . . . . . . . . . . . . . . . . . . . . .$150,000

Business operating expenses. . . . . . . . . . . . . . . . . . . . . . . . . . . . .210,000

Interest income from investments. . . . . . . . . . . . . . . . . . . . . . . . .7,000

Casualty loss. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4,000

Interest expense on home mortgage. . . . . . . . . . . . . . . . . . . . . . .9,000

Long-term capital gains (nonbusiness) . . . . . . . . . . . . . . . . . . . . .3,000

Long-term capital loss (nonbusiness). . . . . . . . . . . . . . . . . . . . . . .5,000

Long-term capital gains (business) . . . . . . . . . . . . . . . . . . . . . . . .1,000

The casualty loss represented the uninsured theft of R's personal auto worth $4,100 ($9,000 adjusted basis).

a. Compute R's net operating loss for 2017.

b. Assuming R carries the loss back to 2015, when must the corrected return for 2015 be filed?