Answer:
283,957 cameras
Step-by-step explanation:
Profit generated =  cost  - Revenue
Given 
Cost function C(x) = 3.5x + 185000
Revenue function R(x) = x(125 -0.0005x)
Profit =  $6,000,000
To get the value of x, we will substitute the given parameters into the formula as shown;
 $6,000,000 = 3.5x + 185000 - x(125 -0.0005x)
 $6,000,000 = 3.5x + 185000 - 125x +0.0005x²
0.0005x²-121.5x + 185000 - 6,000,000 = 0
0.0005x²-121.5x-5815000 = 0
On solving the resulting quadratic equation
x = 283,956.91736581  and -40956.917365805
Ignoring the negative value, the minimum camera that must be sold is approximately  283,957 cameras