УМОЛЯЮ ПОМОГИТЕ МНЕ! МАТЕМАТИКА 6 КЛАСС!

1. $\frac{n}{4} +1= \frac{7}{4} \\ \frac{n}{4}= \frac{7}{4} - 1= \frac{7-4}{4} = \frac{3}{4}$

2. $20-5(x-4)=65 \\ 20-5x+20=65 \\ 40-5x=65 \\ -5x = 65-40 \\ -x= 25 \\ x=-25$

3/ $( 3\frac{2}{5} - 9,6) : \frac{1}{15}= \\ 1) 3 \frac{2}{5} - 9,6 = 3 \frac{2}{5} - 9 \frac{6}{10} = 3 \frac{4}{10} -9\frac{6}{10} = 2 \frac{14}{10} - 9\frac{6}{10}= -7 \frac{8}{10} = -7 \frac{4}{5} \\ 2) -7 \frac{4}{5}:\frac{1}{15} = -\frac{39}{5} :\frac{1}{15} = -\frac{39*15}{5*1} = - \frac{39*3}{1*1} = -\frac{117}{1} =-117$