What is the equation if x=1 and y=16/3

There may be more than one way in which to answer this question.  I will assume that the "equation" is a linear one:  f(x) = mx + b.

Then (16/3) = m(1) + b
This is one equation in two unknowns, so it does not have a unique solution.  Was there more to this problem than you have shared?

If we assume that the y-intercept (b) is zero, then y = mx, and 

16/3 = 1m, so that m = 16/3, and so   y = (16/3)x.