Percent problems

Titanic sailed to New York on April 10, 1912. Among the $2200$ people on board there were Class I, Class II, Class III passengers and the crew. The pie chart shows the Titanic percent composition (to $1\mathrm{\%}$ accuracy). By what percentage is the number of the third-class passengers bigger than the number of the crew?

There are $40$ students in the class, including $18$ girls. What percentage of students in this class are boys?

Support for a political party X in March $2017$ was $24\mathrm{\%}$, and in September $2017$ it was $30\mathrm{\%}$. Party X noted an increase in support by:

How much pure gold contains a ring weighing $7$ grams if the gold fineness is $750$? (That means, the gold content is $75$ percent.)