If I am reading this correctly, you are given the differential equation, $\displaystyle m\frac{dv}{dt}= -\frac{1}{2}\rho AC_{\rho}\nu^2- k\frac{dm}{dt}$ for rocket propulsion. We are further told that the fuel, which accounts for the mass, m, is being used at rate 6 kg/sec so, since m= 3000 initially, m(t)= 3000- 6t. You are first asked to substitute that for m as well as given values for $\displaystyle \rho$, A, $\displaystyle C_\rho$, etc. to arrive at the equation $\displaystyle \frac{d\nu}{dt}= \frac{18000- 0.15\nu^2}{3000- 6t}$. Have you done that?
You are asked to use "Euler's method in Excel" to solve that equation. Do you have "Excel" on your computer? Do you know what "Euler's method" is? Do you know how to implement "Euler's method" in "Excel"? (I don't use "Excel" myself but I bet it has a built in "Euler's method" command!)