How do I set up this equation?

Question

If Y varies directly as X and Y = 12 when X = 3, find Y when X = 16

Answer 1

If y varies directly with x, then there must be some number "k" such as:
y=k*x
Y = 12 when X = 3...So?
12=k*3
k=12/3
k=4
Since you found k, then you can plug in to find Y.
Y= 4*16
Y= 64