For a non-resident:
![C_(nr)=8d+2.5d=10.5d](https://img.qammunity.org/2019/formulas/mathematics/middle-school/jlp6t3tn6pjwdddf2plvu1shmc8u6t9364.png)
For a resident:
![C_(r)=114+1d](https://img.qammunity.org/2019/formulas/mathematics/middle-school/spejtlfeirgcg2ksup765tdzqtj7b8lc35.png)
We want to know the number of days
such that the two costs are equal ie
![\C_(nr)(d)=C_(r)(d)\](https://img.qammunity.org/2019/formulas/mathematics/middle-school/erz8sjgj6jd50m38yi3xkyfqlq61bzvmrg.png)
To do this set the two costs equal to each other:
![C_(nr)=C_(r)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/fnmyj8sd1woidlj1dmh214n6ag35dh2gwv.png)
![10.5d=114+1d](https://img.qammunity.org/2019/formulas/mathematics/middle-school/w68cvw3fswchnkzxq6thq5enjirb7uove5.png)
And solve for d:
![10.5d-1d=114+1d-1d](https://img.qammunity.org/2019/formulas/mathematics/middle-school/4tq0nzyn8he5c0nz2670i7dhkwxuu4crhu.png)
![9.5d=114](https://img.qammunity.org/2019/formulas/mathematics/middle-school/z39wi272qomo14cnhwuk7p7sxu3knqvsqq.png)
![d=(114)/(9.5)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/bfxogcfhlm0wrrlvteqb10lbttqqcd88sz.png)
![d=12](https://img.qammunity.org/2019/formulas/mathematics/college/wenlvkl3q7tyka4zi3bgcxsn3i3jb37ghk.png)
The costs will be equal when a resident and a non-resident each use the beach for 12 days.