There Are Presently $N = 300$ Cases of Bangkok Flu, and the Number Is Growing by and the Number

Multiple Choice

There are presently $N = 300$ cases of Bangkok flu, and the number is growing by 40 new cases every month. Rewrite the rate in mathematical notation.

A) $\frac { \mathrm { d } N } { \mathrm {~d} t } = \frac { 2 } { 15 }$
B) $\frac { \mathrm { d } N } { \mathrm {~d} t } = 40$
C) $\mathrm { d } N = 40$
D) $\frac { \mathrm { d } N } { \mathrm {~d} t } = 7.50$
E) $N = 40$