a. a+(25/100)*a = 253.000 => 4a+a = 1012000 => 5a= 1012000 => a=202.400
b. 253000-(a/100)*253000 = 202400
2530a = 253000-202400
2530a = 50600
a= 20 %
c. a+ (15/100)*a+ (10/100)*[a+(15/100)*a] = 253000
a+15a/100+115a/1000=253000
(1000a+150a+115a)/1000 = 253000
1265a=253000=> a=200