a)
p + 20%p = 67200
p + p/5 = 67200
5p + p = 336000
6p = 336000
p = 56000 lei pret initial
b)
67200 - x%67200 = 56000
67200 - 56000 = 672x
11200 = 672x
x = 16,(6) %
c)
p + 5%p + 25%(p + 5%p) = 67200
p + 0.05p + 0.25(p + 0.05p) = 67200
p + 0.05p + 0.25p + 0.0125p = 67200
1.3125p = 67200
p = 51200 lei