What is the percent of change from 4,000 to 2,000?

Given abcd ac=38 and ae=3x+4 find the value of x

The length of a shadow of the building is 36m. the length of the pole, which is perpendicular to the ground, is 1.9m. the length of the pole's shadow is 1.52m. what is the height of the building?

:24% of students in a class are girls. if there are less than 30 students in this class, how many students are there? how many girls are there?