Answer
$1.8$ hrs, or (H)
Work Step by Step
Here, we are looking for the value of $x$ where $C(x) = 1.3$. So, we set the equation for $C(x)$ equal to $1.3$ and solve for $x$:
$C(x) = \frac{10}{2x^2+1} = 1.3$
Multiply both sides by $2x^2+1$:
$10 = 2.6x^2+1.3$
Isolate the $x^2$ term:
$2.6x^2 = 8.7, x^2 = 3.35$
Solve for $x$ by taking the square root of 3.35, only worrying about the positive answer, because in this case, time after injection would never be negative.
$x = \sqrt{3.35} = 1.83$
