translate the following variation statement below to its corresponding variation equation use k as the constant of variation .
1. the perimeter (P) of an equilateral triangle varies directly as the length of the side (S).
2.the number of test papers (T) a teacher can check in an hour varies directly as the amount of items in a test (I).
3. the cost per person (c) of hiring a taxicab varies inversely as the number of persons (N) sharing the cost.
4.the time (t) required to empty a tank varies inversely as the rate (r) of pumping.
5.the amount of heat (h) put out by an electrical appliance varies jointly as time (t), resistance (r) in the circuit and the square of the current (I).
6.the volume of a cone (V) varies jointly with its height (h) and the square of its base (r)
7.the number of telephone. calls (N) made between two cities varies jointly with the populations (P1) and (P2) of the cities and inversely with the distance (d) between them.​