Given the equation
![y=2x+51](https://img.qammunity.org/2023/formulas/mathematics/college/qw6gg2nhq8d7bm6jl7c4i4ppmecocul9om.png)
Notice that it is a linear equation
The change per day in the road's length is given by the slope of the line which is the constant that accompanies the x-term.
Therefore, the answer to part 1) is 2 miles.
On the other hand, set x=0 (zero days since the crew started working); then,
![\begin{gathered} y=2\cdot0+51 \\ \Rightarrow y=51 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/do6u52q3l0q2lkfce9iyympnxx5tnrg1ao.png)
Thus, the initial length of the road is 51 miles.