Answer:
4d+56=L
4(39)+56=L
L=212
Step-by-step explanation:
4 miles per day added on to the already existing 56 miles equals the total length.
When subbing in 39 for the number of days (or variable "d" in the equation), and following the order of operations, you get 212 miles of road total at the end of the 39 days.