I need a full explanation about why we solve it like that

Concept Review Following data have been assembled on April 30, 2021 for analysis of possible adjustments for the business. a) Insurance expired during April is $300. b) Supplies on hand on April 30 are $1,350. c) Depreciation of office equipment for April is $330. d) Accrued receptionist salary on April 30 is $120. e) Rent expired during April is $1,600. f) Unearned fees on April 30 are $2,500