Answer:
dividends paid during 2015:
preferred stock dividends = $20,000, dividend per preferred stock = $0.25
common stock dividends = $0, dividend per common stock = $0
dividends paid during 2016:
preferred stock dividends = $28,000, dividend per preferred stock = $0.35
common stock dividends = $0, dividend per common stock = $0
dividends paid during 2017:
preferred stock dividends = $30,000, dividend per preferred stock = $0.375
common stock dividends = $170,000, dividend per common stock = $0.85
dividends paid during 2018:
preferred stock dividends = $30,000, dividend per preferred stock = $0.375
common stock dividends = $320,000, dividend per common stock = $1.60
Since the preferred stocks are not cumulative, any preferred dividends that are not paid during a year will not be paid in future years.