x-pretul initial
10% din x= 10/100 * x= 1/10 * x= x/10-prima marire
x+x/10 = (10x+x)/10= 11x/10-noul pret
20% din 11x/10= 20/100* 11x/10= 1/5 * 11x/10 = 11x/50 -a 2a marire
11x/10 + 11x/50= (55x+11x)/50 = 66x/50 -noul pret
66x/50=528
x=50*528/66
x=50*8
x=400