To write 3000 as a fraction you have to write 3000 as numerator and put 1 as the denominator. Now you multiply numerator and denominator by 10 as long as you get in numerator the whole number.
3000 = 3000/1 = 30000/10
And finally we have:
3000 as a fraction equals 30000/10
Δx (delta x) is about a secant line, a line between two points representing the rate of change between those two points. That's a "differential" (between the two points).
dx is about a tangent line to one point, representing an instantaneous rate of change. That makes it a "derivative."
Thw answer to your Problem would be A
0.007, also known as the thousandths place in decimals.