SAT Question 6310adbc: Ratios Rates Proportional Relationships And Units answer and explanation with Desmos solution

Choice D is correct. It's given that the ratio of $t$ to $u$ is $1$ to $2$. Since $t=10$, it follows that the ratio of $10$ to $u$ is also $1$ to $2$. The relationship between these ratios can be represented by the proportion $\frac{10}{u}=\frac{1}{2}$. Multiplying both sides of this equation by $2$ and then by $u$ yields $20=u$.