The class is about heat, waves, and light. The website wants exactly the perfect answer and in the same metric system units that are stated on the calculators that are on the picture for the question, if not, it'll mark it wrong.

Set 17 Problem 2 Check out the result of Problem 3] in Chapter 34 {4m edition) or Problem 27 in Chapter 35 (3rd edition). You may assume that the thickness of the air gap between the convex lens surface and the at glass is much less than the radius of curvature of the lens