Some male peakcocks used to have bright and large tails while others had dull, smaller tails. Female peacocks will only mate with the ones that have the brightest and largest tails. Explain how this would impact the offspring of male peacocks over time.

Over time, most males will have bright and large tails. Females only mate with males carrying these traits, and so natural selection will favor them.

Explanation:

Bright and large tails are traits that reflect the genetic quality of males. So individuals with the most vibrant color and length express better capabilities of finding food, competing for resources, competing for males, among others, are the best option to mate and to ensure successful offspring.

The brightest and largest tails are, the better chances males have to mate and pass their genes to the following generations. So the organism spends energy and resources to produce more vibrant colors and longer feathers to enhance mating chances.

Females must ensure their reproductive success, so sexual selection is the pressure modeling males in this species. Females will only choose individuals with the better genetic charge to mate -individuals with brightest and largest tails-, so their progeny can have better genes and higher survival probabilities.

Males with the brightest and largest tails will mate and reproduce. They will pass their genes to their progeny. Male offspring will also have bright and large tails because they inherit these conditions from their parental. These male offspring will also pass their genes to the progeny, and so on. The frequency of the alleles that express these traits will increase in the population. Natural selection is favoring these alleles. So over time, there will be much more individuals with bright and large tails than individuals with dull and small tails.

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.