Which is a possible way to rewrite the equation y=3x+3b to solve for b?

you could rewrite it as 3b=y-3x

Subtract 3x on both sides and u get 3b=y-3x then divide 3 on both sides to get b alone

b=(y-3x)/3

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