If lucy need 20 skeins of yarn

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?

Evaluate the expression for the given value of the variable 7a - 4a for a =8

What is the axis of symmetry of the function f(x)=-(x+ 9)(x-21)