posted by Pam .
The number N, in millions, of hearing impaired individuals of age x can be approximated by:
N = -0.00006x^3 + 0.006x^2 - 0.1x + 1.5
Approximate to the nearest million the number of hearing impaired individuals of ages 45 - 70.
Because x is a discrete variable,as in 45,46, 47, ... it cannot be integrated by continous integration. But numerical methods can be used. I don't know if you have done that. I also assume you are not using the program MATHLAB.
So, I hate to tell you to add up all the N for x=45,46,47, ...
I did it on a numerical integration
http://mste.illinois.edu/activity/integration/#description and got 99 million. Here you do it, and in that web page paste this in the formula
formula: -.00006*x^3 + .006*x^2 - .1*x+1.5
left endpoint; 45
right enpoint: 70
number of partitions: 25 ie, (70-45)