If y varies directly as x, and y is 400 when x is r and y is r when x is 4, what is the numeric constant of variation in this relation?

So than y varies directly with x this mean y = x 
so than y=400 when  x=r andy = r when  x = 4 

y=400 x=r
y =r x=4

bc. we know that y varies directly as x so y=nx so r= 4/400 = 1/100 

the numeric constant is r = 1/100