Помогите пожалуйста решить задание по геометрии 7 класс

К раcтвору содержащему 40 грамм соли,добавили 200 грамм води,после чего его концентрация уменьшилась на 10%. Сколько воды содержал раcтвор. какова была его концентрация.

Определите диапазон длин волн, воспринимаемых человеком. Звук распространяется в воздухе при температуре 20 градусов С. Скорость звука в воздухе 340м/с.

переведите пожалуйста!!:)

I started school the following September, and my brother went to kindergarten. I still remember my first day at school. I even remember that there were 38 students in my class – but of course I’ve long forgotten most of their names by now.
We lived in the same flat all the time I was at school. I only moved house again when I started university in 2003. I decided to study forestry so I had to move to a town near the border. Rents were quite expensive, so I decided to move into a shared flat. Five of us rented a large flat in the city centre, and shared all the housework. I had the time of my life! I’m still living in the same town, but I’m sharing with just one person now. It’s more comfortable but I often miss the big parties we used to have at the other place.