(original cost) - (original cost)*20% = $12,590 (the given information)

(original cost)(100% - 20%) = $12,590 (factor)

(original cost)(80%) = $12,590 (subtract the percentages)

(original cost)(80/100) = $12,590 (convert to fraction)

(original cost)(.80) = $12,590 (convert to decimal)

(original cost) = $12,590/.80 (divide both sides by .80)

(original cost) = $15,737.50

(original cost)(100% - 20%) = $12,590 (factor)

(original cost)(80%) = $12,590 (subtract the percentages)

(original cost)(80/100) = $12,590 (convert to fraction)

(original cost)(.80) = $12,590 (convert to decimal)

(original cost) = $12,590/.80 (divide both sides by .80)

(original cost) = $15,737.50