Hey there! I'm happy to help!
A great way to see the direction a river runs is to see the two endpoints of that river. Whichever one is higher will most likely determine the direction the river flows just due to gravity. If a river starts in a mountain and ends in a lake that is north of the mountain, you can expect that the river flows north and not south just due to gravity.
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MISSOURI RIVER
We see that the West end this river is in the Rocky Mountain area and the other end is in the plains/plateau area. The Rocky Mountains are much higher than plains, so that means that that is where the river starts, and it will be flowing away from that. We see that the direction it goes is generally East.
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COLORADO RIVER
The West End of this river is in the plateaus and highlands while the other is in the Rocky Mountains. The Rocky Mountains, the high point, at the East end of the river, so it is going to be flowing West due to gravity.
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RIO GRANDE
This river also starts in the Rocky Mountains and appears to flow down into the highlands and plains. Since the Rocky Mountains are at the North part of this river, it is going to be flowing South.
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Have a wonderful day and keep on learning! :D