simplify 2x^7-9x^7

Question

and

80 dollar shirt 30% off = ?
(how do i put this together)

Answer 1

2 x ^ 7 - 9 x ^ 7 = - 7 x ^ 7

100 % - 30 % = 70 % = 70 / 100 = 0.7

80 * 0.7 = 56 $