One day, I decide to run to the park. On the way there, I run at a rate of $x^2$ miles per hour for $3$ hours. On the way back, I take the same path and jog at a slower rate of $16 - 4x$ miles per hour so that it takes me $4$ hours to get home. Given that $x > 0$, what is $x$? Express your answer as a common fraction.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
One day, I decide to run to the park. On the way there, I run at a rate of $x^2$ miles per hour for $3$ hours. On the way back, I take the same path and jog at a slower rate of $16 - 4x$ miles per hour so that it takes me $4$ hours to get home. Given that $x > 0$, what is $x$? Express your answer as a common fraction.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
\frac{8}{3}
One day, I decide to run to the park. On the way there, I run at a rate of $x^2$ miles per hour for $3$ hours. On the way back, I take the same path and jog at a slower rate of $16 - 4x$ miles per hour so that it takes me $4$ hours to get home. Given that $x > 0$, what is $x$? Express your answer as a common fraction.
train