Please show me what is the rate of growth of R with respect to small values, and a precise definition of what is meant by "small values of r"

An ellipse has equation r-/3 + y-/4 =7. A rectangle with sides of length r and r/2 is removed from its centre to leave a region with area R(r) - in other words, R is a function of r as in the previous question. What is the rate of growth of R with respect to small values of r? Part of the answer to this question will involve giving a precise definition of what is meant by "small values of r"