You can do this by completing the square
x^2 - 14x + y^2 + 8 = 16
(x - 7)^2 - 49 + (y + 4)^2 - 16 = 16
(x - 7)^2 + (y + 4)^2 = 16 + 16 + 49 = 81
so the center is at (7 , -4) and radius = sqrt81 = 9
50km to 80km is 30km
10c to -80c is -90c
and since it linear (Which means the change is constant or the same)
every 10 km show a -30c decrease
so
60 km is -20c
70km is -50c
answer is c
1.6 × 1.6 × 1.6 × 1.6 = 6.5536
