Answer:
$15.63 ≤ x ≤ $54.365
Step-by-step explanation:
Profit of the phone company is modeled by the equation,
p(x) = -50x² + 3500x - 2500
For the profit of at least $40000,
-50x² + 3500x - 2500 ≥ 40000
-50x² + 3500x ≥ 40000 + 2500
-50x² + 3500x ≥ 42500
-x² + 70x ≥ 850
x² - 70x + 850 ≤ 0
By quadratic formula,
x - intercept of the inequality will be,
x = [tex]\frac{-(-70)\pm \sqrt{(-70)^2-4(1)(850)}}{2(1)}[/tex]
x = [tex]\frac{70\pm \sqrt{1500}}{2}[/tex]
x = 15.635, 54.365
Therefore, $15.635 ≤ x ≤ $54.365 will be the range of cost for which profit will be at least $40000.