the unit rate is the same slope
to calculate the slope we only need two points and this formula
![m=(y2-y1)/(x2-x1)](https://img.qammunity.org/2023/formulas/mathematics/high-school/wt3vklmulg2853jxzclws9uvfaplhmpgv7.png)
where (x2,y2) is a right point from (x1,y1)
I can take two any points for this case i will use (1,5) and (3,15)
we can look (3,15) is right from (1,5) so (3,15) is (x2,y2)
now, replacing
![\begin{gathered} m=(15-5)/(3-1) \\ \\ m=(10)/(2) \\ \\ m=5 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/vvl2vfjmfh3brge929j7zbv2djr3b0cumx.png)
4. how do you know?
the unit rate is the slope, so by formula we can find it
and 5 is the change per unit, we can notice when add a unit of days the big smiles incresses by 5 everytime