10 points for the help of this pre-algebra word problem. Please be specific how you got the answer for #4.?

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 just want to know how you got your answer for the expression part.

* The formula to use/plug is 2.1n+3.7
P.S. They are asking for two questions but exactly how you explain it to them? Please explain how you got one answer to the next.
I meant that *they are asking for 2 answers*; not asking for two questions.