I have the next diferential equation: $\frac{dv}{dt} = g -\frac{c}{m}v$
Given $v(0)=0$, the solution is: $v(t) = \frac{gm}{c}(1-e^{-\frac{c}{m}t})$
Then they ask me to obtain a formula for $c$ in terms of the other values, assuming that I have the values of $m$ and $v(t)$, but I can't clear $c$ from the function of the solution.