[tex]t=\dfrac{s}{v}[/tex]
Time, she spent driving the first 200 miles:
[tex]\dfrac{200}{x}[/tex]
Time, she spent driving the second 200 miles:
[tex]\dfrac{200}{1.5\cdot x}[/tex]
Total time:
[tex]\dfrac{200}{x}+\dfrac{200}{1.5\cdot x}=\dfrac{200}{x}\cdot \dfrac{1.5}{1.5}+\dfrac{200}{1.5\cdot x}=\dfrac{300}{1.5\cdot x}+\dfrac{200}{1.5\cdot x}=\dfrac{500}{1.5\cdot x}=\boxed{\dfrac{1000}{3\cdot x}}[/tex]