Answer
$12\space oz$ orange juice contains $145.5\space mg\approx146\space mg$ of vitamin C.
Work Step by Step
Write a proportion to model the situation. You can set up the proportion so that the numerators have the same units and the denominators have the same units. Then solve the proportion.
$\therefore \frac{8\space oz}{97\space mg}$.
Now let's assume that the other cup of juice contains $x$ milligrams of vitamin C.
Let's equate the proportionality,
$\therefore \frac{8\space oz}{97\space mg}= \frac{12\space oz}{x}$.
Cross multiplying,
$\therefore {x}=\frac{12\space oz\times 97\space mg}{8 \space oz}$
$\therefore x = 145.5 \space mg$.
So, $12\space oz$ orange juice contains $145.5\space mg\approx146\space mg$ of vitamin C.
