Function or not a function?

Not a function.

Step-by-step explanation:

There must only be one output per input but here we see the input 18 has two outputs ; 3 and 15 therefore this is not a function.

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

go and ask your mom to you