What is y_c when finding y_R?

Homework Statement

During the calculation of yR in fluid mechanics problem, hydrostatic force on a plane surface

Homework Equations

yR = yc+$\frac{I_xc}{y_c×A}$

The Attempt at a Solution

I can see how it is calculated but I've read through the chapter and I don't see how it is described. The textbook is Fundamentals of Fluid Mechanics (6th Ed.) by Munson.

Attachments

• fluids example.JPG
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