How do i solve special right triangles

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?

The students in a class were asked how many siblings they have. the data obtained is represented in the dot plot. the number of students who have no siblings is . the number of students who have three or more siblings is .

3/8 of the students in ms. mull’s class ride the bus. if there are 24 students in the class, how many students ride the bus?