(21,5+y:1/2)x15=450,3-0
(21,5+y:1/2) =450,3:15(tìm thừa số)
21,5+y:1/2 =30,02
21,5+y =30,02:1/2
y =30-21,5
y =9
450,3 - ( 21,5 + y : 1/2 ) * 15 = 0
=> ( 21,5 + y : 1/2 ) * 15 = 450,3 - 0 = 450,3
=> 21,5 + y : 1/2 = 450,3 : 15 = 30,,02
=> y : 1/2 = 30,02 - 21,5 = 8,52
=> y = 8,52 * 1/2
=> y = 4,26
chúc cậu hok tốt !