There is a jar of green and red marbles. If there are 21 marbles total and the ratio of green to red is 3:4, how many red marbles are there?

There are 12 red marbles

Step-by-step explanation:

green : red : total

3           4       3+4=7

We want a total of 21

21 /7 =3

Multiply by 3

green : red : total

3*3       4*3   7*3

 9         12     21

5

step-by-step explanation:

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