Which expressions are differences of squares?

select each correct answer.

t^2−1

n^2−225

k^2+81

p^2−40

Factor the expression using gcf 9b+45

Factor the polynomial by its greatest common monomial factor.

Aremote-controlled boat can travel at 4 feet per second in calm water. the boat traveled 48 feet with the current, and then it traveled 16 feet against the current in the same amount of time. how fast is the current?