Solve for a.
a+c=r−d
options:
a) a=r−d−c
b) a=r+d−c
c) a=d+r+c
d) a=c+r−d

A. Because you would have to subtract C to isolate a by itself

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

where are the choices?