Suppose y varies directly as x, and y = 7 when x = 2. Find x when y = 21.

Step-by-step explanation:

y = k x X

7 = k x 2

7/2 = k...............1

hence y = 7/2x (substituting eq 1)

y = 21

therefore, x = 2y/7

x = 2 x 21

         7

x = 2 x 3

x = 6    

6.9

step-by-step explanation:

simple math really

6 1/2 times 0.6 = 3.9

but if you are just doing 6 and not 6 1/2 then the answer is 3.6