(1).

The word y varies inversely with x represents the function , where k is constant.

To find the value of k substitute in the above function.

The function is

The option A is correct.

(3).

The word z varies inversely with x and directly with y represents the function , where k is constant.

To find the value of k, substitute in the above function.

The function is

To find the value of z, substitute in the above function.

None of these options.