Hello, please consider the following.
x is obviously different from 0 and then, dividing by x is legit.
For the first 105 miles the speed is x, so the time spent is
![(105)/(x)](https://img.qammunity.org/2021/formulas/mathematics/college/b5m5hhqp6ndui3vqr9qu47sv2tvrnyevnt.png)
For the second part, the speed is 1.4 x, so the time spent is
![(105)/(1.4x)=(75)/(x)](https://img.qammunity.org/2021/formulas/mathematics/college/dfm2q2u1a6mw0wp7ephabl5fa0jan47mqt.png)
In total, the time she spent driving is
![(105)/(x)+(75)/(x)\large \boxed{=(180)/(x)}](https://img.qammunity.org/2021/formulas/mathematics/college/p5x00c2yx3fugqcubulvva8iyyyiad3mu1.png)
Thank you.