How many ways can Mrs. Sullivan choose two
students from 27 to help put away calculators at
the end of class?

In 371 ways Mrs. Sullivan choose two  students from 27 to help put away calculators at  the end of class

Step-by-step explanation:

let us assume that Mrs.Sullivan  wants to choose 2 students from a group of 27 students

So ,in the first choice we have  27 students

In the  second choice we have  26 choices

So Mrs.Sullivan has = 27 × 26 = 702 ways

But  each group repeated twice,in order to avoid that we will divide the answer by 2

so we will write

= 702 ÷ 2 = 351 ways

This method of calculation is called Combination

you didn't post any answer choices, so its not 100% clear what your teacher is looking for

however, log(15/7) is equivalent to log(15) - log(7)

i'm using the rule log(x/y) = log(x) - log(y)