Here we have perfectly inelastic collision. Perfectly inelastic collision is type of collision during which two objects collide, stay connected and momentum is conserved. Formula used for conservation of momentum is:

In case of perfectly inelastic collision v'1 and v'2 are same.
We are given information:
m₁=0.5kg
m₂=0.8kg
v₁=3m/s
v₂=2m/s
v'₁=v'₂=x
0.5*3 + 0.8*2 = 0.5*x + 0.8*x
1.5 + 1.6 = 1.3x
3.1 = 1.3x
x = 2.4 m/s
The scale is a rest scale reads the support for is not enough net force.
Answer A sounds about right
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1. Monkeys live in tropical rainforest ecosystems.
2. Animals should be left alone in nature to take part in the balance of the ecosystem, and not upset it. A sudden increase of monkey population, probably due to destruction of rainforests which lead to lesser area of living for them.
3. Monkeys take a huge part in seed dispersal among flesh fruit plants. Without them, it will greatly affect the conservation of the forests.