I mean, I don't know how to explain a generic way to solve this. Ask me about the specific train of thought if you are interested:
7 * 18 + 45 / 3 - 2 = 139
Answer: 8.175
Explanation: 8 is the whole number so set that aside look at 7/40, using simple division solve for a decimal
The expression that does not represent the sum of n and 6 is 6n
5+4=9 9-2=7
7x(-2)= (-14)
your answer is -14