21n over 9n in lowest terms

Rai compares two cable plans from different companies. which equation gives the correct value of mm, the number of months for which plans a and b cost the same?

In the polynomial below, what number should replace the question mark to produce a difference of squares? x2 + ? x - 36

Find the center and the radius of the circle with the equation: x^2-2x+y^2+4y+1=0?