To find the velocity lets integrate acceleration with respect to time. A=-bv-(-Mv(ex)+F^ext)/( Mo - kt) were M is mass F is force... not sure how to integrate it the answer it I guess everything would be like a constant but still dont see how they got the answer i would think of moving all constants out of integral but does not see like they did it that way

v = k/b* v(ex)*[( Mo- M)/ Mo]^-k/b + Vo