Answer:

y=57, when x is 19.
Step-by-step explanation:
We are asked to write an equation of variation where y varies directly as x.
Since we know that a directly proportional equation is in form:
, where k is the constant of proportionality.
Upon substituting x=5 and y= 15 in our equation of variation we will get,



Upon substituting k=3 in the standard equation of variation we will get our desired equation of variation as:
.
Now let us find y, when x is 19.


Therefore, y equals 57, when x is 19.