Respuesta :

7k/3 = 21
x 3       x3
7k = 63
/7      /7
k = 9
(7(9)/3 = 21    =    63/3 = 21    =    21 = 21)
7k÷3=21

Explanation: 
You have to multiply 3 by 21

so you have
7k=63

k = 9