`19/20 × (1/10 + 4/5 × (1 + y) - 3/20) = y`
`=> 19/20 × (1/10 + 4/5 + 4/5y - 3/20) = y`
`=> 19/20 × (1/10 + 4/5 + 4/5y - 3/20) = y`
`=> 19/20 × (9/10 + 4/5y - 3/20) = y`
`=> 19/20 × (3/4 + 4/5y) = y`
`=> 57/80 + 19/25y = y`
`=> 57/80 + 19/25y - y = 0`
`=> y(19/25 - 1) = -57/80`
`=> -6/25y = -57/80`
`=> y = 95/32`
(Chúc bạn học tốt)