Solve the Problem $\mathrm { d } ( \mathrm { x } ) = \frac { \mathrm { Dx } } { \mathrm { x } + 9 } , 0 \leq \mathrm { x } \leq 12$

Solve the problem.
-To calculate the drug dosage for a child, a pharmacist may use the formula $\mathrm { d } ( \mathrm { x } ) = \frac { \mathrm { Dx } } { \mathrm { x } + 9 } , 0 \leq \mathrm { x } \leq 12$ . The child's age is $x$ and the adult dosage is $D$ . What is the dosage for an 3 -year old child if the adult dosage is $10 \mathrm { mg }$ ? (Round to the nearest tenth.)

A) $0.8 \mathrm { mg }$
B) $3.3 \mathrm { mg }$
C) $2.5 \mathrm { mg }$
D) $10.0 \mathrm { mg }$