In how many ways can 3 oaks, 5 pines, and 4 maples be arranged along a property line if one does not distinguish among trees of the same kind?

In a​ bag, there are 11 purple and 7 green marbles. If you reach in and randomly choose 4 ​marbles, without​ replacement, in how many ways can you choose exactly one​ purple?   nothing ways

Suppose we want to choose   3 colors, without replacement, from the   4 colors red, blue, green, and purple.       How many ways can this be done, if the order of the choices does not matter?   How many ways can this be done, if the order of the choices does matter?

In how many ways can you select a group of 7 red cards and 4 black cards from a deck containing 10 red cards and 9 black cards?

A teacher will randomly award three students with extra credit. How many possible ways can the teacher pick these three students from a class of 20 students?