We will imagine a triangle. The hypotenuse of the triangle is the distance between you and the plane. 16 kilometres is the aerial space between you two, in other words its the base of the triangle. 12 km is the length of the third leg of the triangle. We will apply the pythagorean theorem to find the length of the hypotenuse and the distance between you and the plane.
30% of 42 is 12.6$. 42-12.6 = 29.4$ is the price of the pair with discount applied. Tax 7% 29.4 * 7% = 2.06 29.4$ + 2.06$ = 31.46 $ final price with discount and tax applied.
