Y= 99
9. Suppose a varies directly as b, and a = 7 when b = 2. Find b when a = 21.

6

Step-by-step explanation:

Given expression:

    a varies directly as b;

       a ∝ b

 So;

         a  = kb  where k is the constant of proportionality;

if a= 7 and b  = 2;

         7 = 2k

           k =

Now, find b when a = 21

            21  =    x b

           b  = 6