Y varies directly with x and y = 21 when x = 7. Write an equation to represent this relationship.

1) 2/5

2) zero=0/1

3) zero=0/2

4) -4/5

5) undefined=3/0

step by step solution :

step   1   :

1.1     4 = 22

(4)3 = (22)3 = 26

equation at the end of step   1   :

  ((23) • 26)2

step   2   :

equation at the end of step   2   :

  (23 • 26)2

step   3   :

final result :

  218

ya