Answer
See below
Work Step by Step
Given: $n=\frac{635t^2-7350t+27200}{t^2-11.5t+39.4}$
Setting it equal to 720, we have:
$\frac{635t^2-7350t+27200}{t^2-11.5t+39.4}=720\\635t^2-7350t+27200=720t^2-8280t+28368\\85t^2-930t+1168=0$
Solve the equation using the quadratic formula:
$t=\frac{930\pm\sqrt (-930)^2-4\times85\times1168}{2\times85}\approx\frac{930\pm 683.94}{170}$
Thus, $t_1=\frac{930-683.94}{170}\approx1.45\\t_2=\frac{930+683.94}{170}\approx9.49$
Since the condition is $0\leq t\leq 9$, the only solution here is $t=1.45$.
$t$ is the number of years after $1994$; hence in the year 1995 the total
number of CDs shipped is about 720 million.
