помогите решить уравнение)
а)(х+27)-12=42
б)115-(35+у)=39
г)28-t+35=53
А под буквой (в) я сделал)

Определите массу мраморной плиты, размер которой 1,0х0,8х0,1м.

cos((x+pi)/3)=-1

Решить с подробным решением. 

Поставить глагол в нужное время.

1.Mike (to swim) in the swimming-pool while I was sitting and watching him.

2.They went home after they (to solve) this problem.

3.Mike got tired after he (to swim) 3 miles.

4.She (to clean) the rooms before she went out.

5.They (to have dinner) at 2 o'clock yesterday.

6.They said (to learn) Spanish for six months last year, but she can't speak.

7.She (to clean) the rooms when somebody knocked at the door.