Astudent find the slope of the line between (8,17) and (1,4)
she writes 17-4/ 1-8. what mistake did she make

For this case we have that by definition, the slope of a line is given by:

According to the data we have the following points:

Substituting we have:

So, the slope is

The student's mistake was to erroneously subtract the "x" coordinates from the points

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

2nd one in the first row is correct