Percent problems

Of the school's $300$ pupils, $67\mathrm{\%}$ attend the sports club and $42\mathrm{\%}$ attend the music club. $18\mathrm{\%}$ attend both clubs. How many children do not attend any club?

There are $14$ right-handed and $18$ left-handed children among the children attending the ceramic group. Find the difference between percentages of right-handers and left-handers in the group. (Round the result to one decimal place.)

Find the number by $2.5{}^{\text{o}}/{}_{\text{oo}}$ greater than $800$.

The number of permanent residents of a city has decreased by $10\mathrm{\%}$ per year in the last three years. How many residents did the city have three years ago, if we know that the last year the population was $972$?