## Elementary Technical Mathematics

$$1.79\times 10^{-9}.$$
We divide the two numbers as follows: $$\frac{(0.0025)^2}{3500}=\frac{(2.5\times 10^{-3})^2}{3.5\times 10^3} \\ =\frac{6.25\times 10^{-6}}{3.5\times 10^3}=1.79\times 10^{-9}.$$