Given that:
Customer service representation = 75% = 0.75
Programmers = 15% = 0.15
Managers = 10% = 0.1
Average salary of customer service rep = $60,000
Average salary of programmers = $100,000
Target question: what is the average salary of the managers?
Using weighted average,
$$Weighted\ average=a_1b_1+a_2b_2+...+a_nb_n$$
Where a = no. of employees and b = average salary of employee.
Let the average salary of managers = x
Weighted average = total employees average = $100,000
Therefore;
$100,000 = (0.75 * $60,000) + (0.15 * $100,000) + (0.1 * x)
$100,000 = $45,000 + $15,000 + 0.1x
$100,000 - $60,000 = 0.1x
$40,000 = 0.1x
$$x=\frac{40,000}{0.1}=$400,000\ \ \ \ \ \left(Option\ D\right)$$