How to use structure to find the number that written in circles at the center of the decimal?

Which approach to the theory-and-research cycle does the following sequence reflect: (1) specific observations suggest generalizations, (2) generalizations produce a tentative theory, (3) the theory is tested through the formation of hypotheses, and (4) hypotheses may provide suggestions for additional observations?

Angles r and s are complementary. the measure of angle r is 31 degrees. which equation can be used to find angle s?

Which expression is equivalent to 64 - 9x^2?