Is this a relation or function ? what is the domain and range ? what is the input and output ? is it discrete or continuous ?

How do you find principle and simple interest

Which number completes the inequality? 2/3 < _ < 7/9

Suppose that the price p, in dollars, and the number of sales, x, of a certain item follow the equation 4 p plus 4 x plus 2 pxequals56. suppose also that p and x are both functions of time, measured in days. find the rate at which x is changing when xequals2, pequals6, and startfraction dp over dt endfraction equals1.5.