40 square units is teh correct answer
Assuming that each marble can be picked with equal probability, we notice that there is a total of

marbles, of which 2 are red.
So, the probability of picking a red marble is

In fact, as in any other case of (finite) equidistribution, we used the formula

Answer:
80 or 40 linear feet
Step-by-step explanation:
So the total amount of units for sides is 6. (2 2 1 1)
240 ÷ 6 = 40
So if the river was on the long side it would be 80feet, if the river was on the short side it would be 40feet