The answer is 35 different groups.
Steve woke up with a temp of 102.....later, it was 3 degrees lower. This is telling u to subtract...because it is going lower.
102 - 3 = 99...so now he has a temp of 99
Since you're looking for the unit rate, you can start do this:

And yes,

is also correct, it's just switching around the 15
Answer is B:2.3-b
Combine like terms