Construct a function with a rate of change 2/3 and a initial value of 4.

If you recall y=mx+b, the slope-intercept form of a linear equation, the slope, m, is the rate of change of the equation, and the y-intercept is b. 

When switching to function notation, we simply swap y for f(x), and if we start at x=0 and graph in the positive x direction, we've started at whatever initial value exists (the y-intercept value).

Simply: F(x) = 2/3 x + 4