Need help for this word problem... 10 points for being helpful.

4 Question: Based on the answer to question 1 and 2, make a guess on the number of seconds for the green light when the average is 20 vehicles per light cycle. Then calculate the number of seconds USING the EXPRESSION.

# 1 problem: How many seconds should the green light be on if a street averages 5 vehicles in each lane per light cycle? Round to the nearest whole number. The answer is 14 seconds (rounded)

# 2 problem: How many seconds for the green light, to the nearest whole number, if the average is 10 vehicles per light cycle? If the average is 15 vehicles per light cycle? The answer for both of this problem is: 25 seconds (rounded); 35 seconds (rounded).

For problem number 4, I am simply looking how to solve the expression part; since I already know how to do the other problems and get the answer. I have to use order of operation of equation I believe.
* The formula to use/plug is 2.1n+3.7
Please help me solve this. I don't know how to do the problem # 4. P.S. they are asking two questions but what are they asking.

5 vehicles = 14 seconds
10 vehicles = 25 seconds
15 vehicles = 35 seconds
This gets about 10 seconds longer for every 5 vehicles, so for 20 vehicles is should be about 45 seconds (this is the guess part)

2.1n + 3.7 = 2.1*20 + 3.7 = 45.7 seconds, this is the calculation using the expression

First, you need to guess the number of seconds from the answers you got for 1) and 2).
14.2 and 24.7...There's a difference of 10.5...So the next number in the series would be 24.7 + 10.5 = 35.2 (for 15 vehicles) and the one next to that would be 36.2 + 10.5 = 45.7 (for 20 vehicles)
You need to verify how close this answer is by using the expression...
So using n = 20 in the expression, 2.1(20) + 3.7 = 45.7