Which relation is a function?

a.
{(1, 2); (2, 3); (3, 4); (2, 5)}

b.
{(1, 2); (2, 3); (3, 4); (4, 5)}

c.
{(1, 2); (1, 3); (1, 4); (1, 5)}

d.
{(1, 2); (3, 2); (3, 3); (4, 2)}

since the airplane is moving with constant speed then the distance travelled can be calculated by x=u*t

in km/h would be:

x=640*3.5=2.240 km

in m/s would be:

u=640 km/h= 640.000 m/h =640.000/ 3600 m/s =177.8 m/s

t= 3.5 h= 3.5 * 3600 s=12.600 s

then x=u*t= 177.8*12.600= 2.240.280 m