Is this a function help

The variable z is directly proportional to x, and inversely proportional to y. when x is 4 and y is 13, z has the value 1.2307692307692. what is the value of z when x= 9, and y= 20

Which math sentence can be used to determine if the triangle is a right triangle?

The function v(r)=4/3pir^3 can be used to find the volume of air inside a basketball given its radius. what does v(r) represent