Looks as tho' you'll need to derive a function whose input and output values are represented by the given table. First, let's assume that the function is a linear one and that its general form is y=mx+b, where m=slope and b=y-intercept.
Take any two pairs of input-output and find the slope of the line segment that connects these two points. Call the slope "m."
Now use the point-slope form of the equation of a straight line to determine the equation of the line in point-slope form: y-k=m(x-h). You already know the value of m here, and you can pick any set of x- and y-values from the table to replace (h,k).
Good idea to double-check that your equation really does represent every pair of x- and y-coordinates in the table.
Assuming that it does, solve your equation (above) for x. Substitute 16 for y in this equation for x. Calculate the x-value that corresponds to y=16.
