This math topic involves determining the domain of composite functions where the functions are composed of linear functions inside the square root in a rational function setup. Specifically, students are tasked to find the domain of composite functions described by two individual functions; the outer function typically takes the form of a rational expression with a square-root in the denominator, and the inner function is linear. The primary skill practiced is understanding how to determine viable input values (the domain) for these composite functions, visually represented through selecting the correct number line diagram that fits the domain of the composite function.